Multifocal contact lens

ABSTRACT

A contact lens formed from a transparent material having front and rear surfaces, wherein the rear surface has a base curve which is adapted to fit an eye of a wearer of the lens. The front surface has a central zone which has two different cylindrical curvatures which generate first and second central-zone refractive powers differing by an astigmatic factor. The front surface also has an outer zone with two different cylindrical curvatures which generate third and fourth central-zone refractive powers differing by the astigmatic factor, and an intermediary region, intermediate the central zone and the outer zone, having one or more contiguous intermediate zones, each intermediate zone having cylindrical curvatures differing by the astigmatic factor. The refractive powers from the central zone to the outer zone form monotonic progressions of decreasing values.

RELATED APPLICATION

This application is a continuation-in-part to application Ser. No.10/640,114, titled “Multifocal Contact Lens,” filed 12 Aug. 2003, whichis incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to contact lenses, andspecifically to multifocal contact lenses.

BACKGROUND OF THE INVENTION

Accommodation enables a person of normal vision to focus on objects frominfinity to a near point, typically of the order of 25 cm or less fromthe eye. A presbyope has lost the ability to accommodate over such alarge range, and typically requires two corrections: a distancecorrection for focussing to infinity, and a near correction forfocussing to close objects. Corrections, which are typically differentfor each eye, are usually prescribed to a quarter of a diopter, and mayrange between approximately +8 and −8 diopters for both the distancecorrection and the near correction.

Multifocal spectacles provide the two corrections for each eye, as wellas intermediate corrections, in separate regions of one lens. Suchspectacles rely on the fact that the spectacle lenses are relativelyfixed with respect to the eye, so that the spectacle wearer usuallylooks through the higher portions of the lens for distant objects, andthe lower portion of the lens for near objects.

Multifocal contact lenses that provide both corrections for a particulareye in a single lens are known in the art. However, unlike spectaclelenses, contact lenses move with the motion of the eye. Thus, multifocalcontact lenses known in the art use a number of different systems toenable a presbyope to be adequately corrected for viewing both near anddistant objects. Unfortunately, not all of these systems have been wellreceived by users.

U.S. Pat. No. 5,125,729, to Mercure, whose disclosure is incorporatedherein by reference, describes a lens which has, on its front surface, acentral spherical circular area which is surrounded by an annularaspherical area. The central area is responsible for distance vision.The annular aspherical area enables vision at all distances includingreading.

U.S. Pat. No. 5,526,071, to Seidner et al., whose disclosure isincorporated herein by reference, describes a diagnostic contact lens.After diagnosis involving an over-refraction process, the patient isfitted with a prescription lens. The prescription lens has two frontannular aspheric surfaces, or in the case where intermediate vision isto be accommodated, three (or more) front aspheric surfaces. Thedistance vision area is a central area of the lens, while the nearvision area is one of the annular areas in the periphery of the frontsurface of the lens.

U.S. Pat. Nos. 5,619,289 and 5,691,797 to Seidner et al., whosedisclosures are incorporated herein by reference, describe a lens havinga front central aspheric surface for distance vision correction with adiameter of about 1.5-2.5 mm and an eccentricity of about −0.8. A firstannular surface surrounding the central surface is aspheric and has adiameter of about 2.0-3.5 mm. Other annular surfaces have diameters ofabout 2.3-4.0, and 3.5-8.0, and may be spheric or aspheric.

U.S. Pat. No. 5,754,270 to Rehse et al., whose disclosure isincorporated herein by reference, describes a lens having a centralaspheric optic zone with a diopter power equal to the distant powercorrection, plus an add power range of from 2.5 to 2.25 diopters fromcenter outward. There is a second “blending zone” concentric with thecenter zone, that provides a rapid power shift of about −0.5 to about−1.25 diopters over a small distance of about 0-0.2 mm, typically about0.05 mm.

U.S. Pat. Nos. 5,864,379 and 6,540,353 to Dunn, whose disclosures areincorporated herein by reference, describe a lens having a centralspherical circular region that is overcorrected for near vision,typically by about 25%-100%, with a diameter of about 1.0-2.5 mm. Thecentral zone is surrounded by up to three annular aspherical zones, thefirst two having thicknesses of about 0.5 mm, the third having an outerdiameter of about 8 mm.

U.S. Pat. Nos. 6,030,077 and 6,260,966 to Sawano et al., whosedisclosures are incorporated herein by reference, describe a lens havinga central circular spheric region with a first constant power, anintermediate annular aspheric region, and an outer annular sphericregion having a second constant power. The radii of different parts ofthe intermediate region are calculated from two opposing paraboliccurves which smoothly connect to each other and to the constant powersof the center and outer zones.

U.S. Pat. No. 6,116,735 to Wada, whose disclosure is incorporated hereinby reference, describes a lens having zones which alternate betweennear- and far-correction zones. Typically there are four zones. Acentral near-vision zone is approximately 1-2 mm diameter, and the otherzones have equal widths of about 0.63 mm.

Other systems for correcting vision are known in the art. For example,U.S. Pat. No. 5,695,509 to El Hage, whose disclosure is incorporatedherein by reference, describes a mold for reshaping the cornea.Curvatures of surfaces of the mold are modifications of the cornealtopography of the mold wearer, and include a flattened pressure zone anda relief zone designed to receive displaced corneal tissue.

U.S. Pat. No. 5,771,088 to Perrott, whose disclosure is incorporatedherein by reference, describes a contact lens for improving peripheralvision. The contact lens is formed as an “aplanatic fit” lens (stated tobe a lens having an aspheric, preferably hyperbolic or parabolic, frontsurface to correct spherical aberration). In addition to an aplanaticcentral zone, the lens has an outer spherical zone.

Correct provision of a multifocal contact lens for a specific eyetypically requires knowledge of both the near and far correction of theeye of the patient. Since both corrections are typically prescribed towithin a quarter of a diopter, it will be appreciated that there are alarge number of near- and far-combinations. Notwithstanding that certainmultifocal lenses known in the art, including some of those describedabove, claim to be suitable for ranges of prescriptions, there is a needfor an improved multifocal contact lens.

SUMMARY OF THE INVENTION

In some embodiments of the present invention, a contact lens acts as amultifocal lens for correcting vision, typically the vision of apresbyope. A front surface of the contact lens comprises a plurality ofcurved zones which, when taken with a base curve of a rear surface ofthe lens, have different powers, the different powers decreasingmonotonically from a central to an outer zone of the lens. The overalleffect of the decreasing powers enables a wearer of the lens to clearlysee both near and far objects.

In one embodiment, the contact lens also corrects astigmatism. Each ofthe zones has different cylindrical curvatures along two respectiveaxes, the difference in curvatures being selected to compensate forastigmatism of the wearer. The central zone, taken together with a basecurve of the lens, is implemented to correct near vision of the wearer.

In an alternative embodiment, one or more of the zones of the contactlens are formed with one or more non-circular edges, so as to alsoenhance peripheral vision. Typically each non-circular zone is anelongated oval. The elongation of the zone enhances the peripheralvision of the lens wearer in the direction of the elongation, and bychoosing which zones are elongated, the peripheral vision for near, far,or intermediate-distant objects may be enhanced. The selectiveenhancement of peripheral vision may be advantageously used by lenswearers involved in specific activities, such as drivers requiringenhanced horizontal peripheral vision for far objects, or basketballplayers requiring enhanced vertical peripheral vision for intermediateobjects.

In a further embodiment of the present invention, a mold is provided,which when placed on the cornea of a user of the mold, alters the shapeof the cornea to correct the mold user's vision. The mold comprises asurface having a plurality of generally concentric discrete zones. Eachof the zones is curved. A central zone is adapted to shape the cornea ina central corneal region to have a central zone refractive power thatcorrects near vision of the eye. The one or more other zones are adaptedto shape the cornea to form respective regions that, in progressing fromthe central corneal region to an outer region, have monotonicallydecreasing refractive powers. After removal of the mold from the cornea,the decreasing corneal regional refractive powers enable the usr tofocus both near and far objects.

There is therefore provided, according to an embodiment of the presentinvention, a contact lens, including a transparent material having frontand rear surfaces,

wherein the rear surface has a base curve which is adapted to fit an eyeof a wearer of the lens, and

wherein the front surface includes:

a central zone which has a first cylindrical curvature along a firstaxis and a second cylindrical curvature, different from the firstcylindrical curvature, along a second axis, and which, together with thebase curve, is configured to generate a first central-zone refractivepower along the first axis and a second central-zone refractive poweralong the second axis, the first and second central-zone refractivepowers differing by an astigmatic factor;

an outer zone which has a third cylindrical curvature along the firstaxis and a fourth cylindrical curvature, different from the thirdcylindrical curvature, along the second axis, and which, together withthe base curve, is configured to generate a first outer-zone refractivepower along the first axis which is less than the first central-zonepower and a second outer-zone refractive power along the second axiswhich is less than the first outer-zone refractive power by theastigmatic factor; and

an intermediary region, intermediate the central zone and the outerzone, including one or more contiguous intermediate zones, eachintermediate zone having a respective fifth cylindrical curvature alongthe first axis and a sixth cylindrical curvature, different from thefifth cylindrical curvature, along the second axis, so that the one ormore intermediate zones, together with the base curve, generaterespectively one or more first intermediate-zone refractive powers alongthe first axis defining a first monotonic progression of decreasingrefractive power from the first central-zone refractive power to thefirst outer-zone refractive power, and one or more secondintermediate-zone refractive powers along the second axis defining asecond monotonic progression of decreasing refractive power from thesecond central zone refractive power to the second outer zone refractivepower.

Optionally, the base curve has a seventh cylindrical curvature along athird axis, and an eighth cylindrical curvature along a fourth axis.

Typically, the first central-zone refractive power and the secondcentral-zone refractive power are selected to correct near vision of thewearer, and the first outer-zone refractive power is betweenapproximately 1 diopter and approximately 2.5 diopters less than thefirst central-zone power.

In one embodiment, the central zone is substantially circular, andtypically the diameter of the central zone is approximately 2.5 mm.

In an alternative embodiment, the first monotonic progression includes afirst smooth progression defined by a first algebraic function givingvalues of the one or more intermediate-zone refractive powers in termsof the first central-zone refractive power and the first outer-zonerefractive power, and wherein the second monotonic progression includesa second smooth progression defined by a second algebraic functiongiving values of the one or more intermediate-zone refractive powers interms of the second central-zone refractive power and the secondouter-zone refractive power.

Typically, the one or more intermediate zones include two or moreintermediate annular zones having different powers, and the two or moreintermediate zones have approximately equal widths.

The monotonic progression may include a progression chosen from a linearprogression, a geometric progression, and a logarithmic progression.

Optionally, the base curve consists of a spherical curve having a singleradius of curvature.

In some embodiments at least one of the central zone, the outer zone,and the intermediary region are configured to maintain the contact lensin a preset alignment.

There is further provided, according to an embodiment of the presentinvention, a contact lens, including a transparent material having frontand rear surfaces,

wherein the rear surface includes a base curve which is adapted to fitan eye of a wearer of the lens, and

wherein the front surface includes:

a central zone which, together with the base curve, is configured togenerate a central zone refractive power;

an outer zone, which has the form of an outer annulus surrounding thecentral zone, and which, together with the base curve, is configured togenerate an outer zone refractive power which is less than the centralzone power; and

an intermediary region, which has the form of an inner annulusintermediate the central zone and the outer zone, the intermediaryregion having one or more contiguous intermediate zones which areconfigured, together with the base curve, to generate respective one ormore intermediate zone refractive powers defining a monotonicprogression of decreasing refractive power from the central zone to theouter zone,

so that the central zone, the one or more intermediate zones, and theouter zone are separated from each other by edges, at least one of whichis non-circular.

Typically, the central zone refractive power is selected to correct nearvision of the wearer and the outer zone refractive power is betweenapproximately 1 diopter and approximately 2.5 diopters less than thecentral zone power.

In one embodiment the at least one non-circular edge is oval, and anaxis of the oval is selected to enhance peripheral vision of the wearerin a direction defined by the axis.

Alternatively, at least one of the edges is circular.

There is further provided, according to an embodiment of the presentinvention, a mold for shaping a cornea of a user of the mold, the moldincluding a surface which includes:

a central zone which is curved and which is adapted to shape the corneain a central corneal region to have a central zone refractive power;

an outer zone which is curved and which is adapted to shape the corneain an outer corneal region to have an outer zone.refractive power whichis less than the central zone refractive power; and

an intermediary region, intermediate the central zone and the outerzone, having one or more contiguous intermediate zones, each of which iscurved and which is adapted to shape the cornea to have respective oneor more intermediate zone refractive powers defining a monotonicprogression of decreasing refractive power from the central zone to theouter zone.

Typically, the central zone refractive power is selected to correct nearvision of the user, and the outer zone refractive power is betweenapproximately 1 diopter and approximately 2.5 diopters less than thecentral zone refractive power.

There is further provided, according to an embodiment of the presentinvention, a contact lens, including a transparent material having frontand rear surfaces,

wherein the rear surface includes a base curve which is adapted to fitan eye of a wearer of the lens, and

wherein the front surface includes:

a central circular zone which is spherically curved and which, togetherwith the base curve, is configured to generate a central zone refractivepower;

an annular outer zone which is spherically curved and which, togetherwith the base curve, is configured to generate an outer zone refractivepower which is less than the central zone power; and

an annular region, intermediate the central zone and the outer zone,including one or more contiguous intermediate annular zones, each ofwhich is spherically curved, the one or more intermediate annular zonesbeing configured, together with the base curve, to generate respectiveone or more intermediate zone refractive powers defining a monotonicprogression of decreasing refractive power from the central zone to theannular outer zone.

Typically, the contact lens has dimensions according to any one exampleset out in tables I, II, III, IV, V, and VI below.

In one embodiment, the outer zone refractive power is betweenapproximately 1 diopter and approximately 2.5 diopters less than thecentral zone refractive power, typically the outer zone refractive poweris one of approximately 1.25 diopters and approximately 2.00 dioptersless than the central zone refractive power.

In an alternative embodiment the transparent material between thecentral curved zone and the base curve has a first range of refractiveindices so that the central curved zone together with the base curvegenerates the central zone refractive power, the transparent materialbetween the annular outer curved zone and the base curve has a secondrange of refractive indices so that the annular outer curved zonetogether with the base curve generates the outer zone refractive power,and the transparent material between the one or more contiguousintermediate annular curved zones and the base curve has respective oneor more third ranges of refractive indices so that the one or moreintermediate annular curved zones together with the base curve generatethe respective one or more intermediate zone refractive powers.

There is further provided, according to an embodiment of the presentinvention, a method for forming a contact lens, including:

forming on a transparent material a rear surface having a base curvewhich is adapted to fit an eye of a wearer of the lens; and

forming on the transparent material a front surface including:

a central zone which has a first cylindrical curvature along a firstaxis and a second cylindrical curvature, different from the firstcylindrical curvature, along a second axis, and which, together with thebase curve, is configured to generate a first central-zone refractivepower along the first axis and a second central-zone refractive poweralong the second axis, the first and second central-zone refractivepowers differing by an astigmatic factor,

an outer zone which has a third cylindrical curvature along the firstaxis and a fourth cylindrical curvature, different from the thirdcylindrical curvature, along the second axis, and which, together withthe base curve, is configured to generate a first outer-zone refractivepower along the first axis which is less than the first central-zonepower and a second outer-zone refractive power along the second axiswhich is less than the first outer-zone refractive power by theastigmatic factor, and

an intermediary region, intermediate the central zone and the outerzone, including one or more contiguous intermediate zones, eachintermediate zone having a respective fifth cylindrical curvature alongthe first axis and a sixth cylindrical curvature, different from thefifth cylindrical curvature, along the second axis, so that the one ormore intermediate zones, together with the base curve, generaterespectively one or more first intermediate-zone refractive powers alongthe first axis defining a first monotonic progression of decreasingrefractive power from the first central-zone refractive power to thefirst outer-zone refractive power, and one or more secondintermediate-zone refractive powers along the second axis defining asecond monotonic progression of decreasing refractive power from thesecond central zone refractive power to the second outer zone refractivepower.

There is further provided, according to an embodiment of the presentinvention, a method for forming a contact lens, including:

forming on a transparent material a rear surface including a base curvewhich is adapted to fit an eye of a wearer of the lens; and

forming on the transparent material a front surface including:

a central zone which, together with the base curve, is configured togenerate a central zone refractive power,

an outer zone, which has the form of an outer annulus surrounding thecentral zone, and which, together with the base curve, is configured togenerate an outer zone refractive power which is less than the centralzone power, and

an intermediary region, which has the form of an inner annulusintermediate the central zone and the outer zone, the intermediaryregion including one or more contiguous intermediate zones which areconfigured, together with the base curve, to generate respective one ormore intermediate zone refractive powers defining a monotonicprogression of decreasing refractive power from the central zone to theouter zone,

so that the central zone, the one or more intermediate zones, and theouter zone are separated from each other by edges, at least one of whichis non-circular.

There is further provided, according to an embodiment of the presentinvention, a method for shaping a cornea, including:

providing a mold having a surface which includes:

a central zone which is curved and which is adapted to shape the corneain a central corneal region to have a central zone refractive power,

an outer zone which is curved and which is adapted to shape the corneain an outer corneal region to have an outer zone refractive power whichis less than the central zone refractive power, and

an intermediary region, intermediate the central zone and the outerzone, including one or more contiguous intermediate zones, each of whichis curved and which is adapted to shape the cornea to have respectiveone or more intermediate zone refractive powers defining a monotonicprogression of decreasing refractive power from the central zone to theouter zone; and

applying the mold to the cornea.

There is further provided, according to an embodiment of the presentinvention, a method for forming a contact lens, including:

forming on a transparent material a rear surface including a base curvewhich is adapted to fit an eye of a wearer of the lens; and

forming on the transparent material a front surface including:

a central circular zone which is spherically curved and which, togetherwith the base curve, is configured to generate a central zone refractivepower;

an annular outer zone which is spherically curved and which, togetherwith the base curve, is configured to generate an outer zone refractivepower which is less than the central zone power; and

an annular region, intermediate the central zone and the outer zone,including one or more contiguous intermediate annular zones, each ofwhich is spherically curved, the one or more intermediate annular zonesbeing configured, together with the base curve, to generate respectiveone or more intermediate zone refractive powers defining a monotonicprogression of decreasing refractive power from the central zone to theannular outer zone.

The present invention will be more fully understood from the followingdetailed description of the embodiments thereof, taken together with thedrawings, a brief description of which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates schematic top and cross-section views of a multifocalcontact lens, according to an embodiment of the present invention;

FIG. 2 is a schematic top view of a multirange contact lens, accordingto an embodiment of the present invention;

FIG. 3 shows schematic top views of a number of multirange contactlenses, according to an embodiment of the present invention; and

FIG. 4 is a schematic cross-section of a mold, according to anembodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Reference is now made to FIG. 1, which illustrates schematic top andcross-section views of a multifocal contact lens 10, herein also termedmultirange lens 10, according to an embodiment of the present invention.Lens 10 is typically formed from a hydratable transparent material, suchas Methafilcon A, that is known in the art as being used to producecontact lenses, and that is typically used for producing “soft” contactlenses. Alternatively, lens 10 may be produced from any othertransparent material, such as glass or plastic, that is adapted toproduce contact lenses, such as material known in the art for producing“hard” contact lenses.

After production, dimensions of lens 10 may alter, typically when thematerial of the lens hydrates, to “wet” dimensions, which are thedimensions of the lens under normal use. Unless otherwise stated,dimensions of lens 10 given hereinbelow are wet dimensions.

Lens 10 comprises a near surface 22, which is formed as a base curve tofit the eye of the user of the lens. Except where otherwise stated, thebase curve is herein assumed to be a curve having a single base curveradius of approximately 8.8 mm. Typically, an annular relief 27, havinga width of approximately 0.5 mm, is provided in the base curve for thepurposes of easy fitting to the eye.

A far surface 12 of lens 10 comprises a plurality, typically four, ofspherical zones which provide optical correction for the eye of thewearer. Far surface 12 also comprises another zone 20, which acts as asubstantially optically inactive carrier for the optical zones, andwhich typically has an outer diameter of approximately 14.2 mm,corresponding to the overall diameter of lens 10. A central circularzone 24, having an outer edge 26, typically has a diameter D₁ ofapproximately 2.5 mm. A central zone spherical radius R₁ has a value sothat a central zone refractive power P₁, which is a function of thecentral zone radius and the base curve spherical radius, issubstantially constant and is approximately equal to the near correctionof the lens wearer.

An outer annular zone 18 of surface 12 has an internal diameter D₃ ofapproximately 4.5 mm, and an external diameter D₄ of approximately 9 mm.The outer annular zone is formed to have an outer zone spherical radiusR₄ that, when taken with the base curve, gives an outer zone refractivepower P₄ that is a preset value less than central zone power P₁.Typically, the preset value is a value that is between approximately 1and approximately 2.5 diopters. In the specification and in the claims,referring to a first power (such as P₄) as being less than a secondpower (such as P₁) is to be understood as assuming that the powers aremeasured in real numbers. For example, a preset value of 2.5 dioptersmay generate diopter values of (P₁=+10, P₄=+7.5), (P₁=+1.5, P₄=−1), and(P₁=−10, P₄=−12.5).

Between central zone 24 and outer annular zone 18 are two intermediateannular zones, each typically having a width of approximately 0.5 mm. Afirst intermediate zone 14 with an outer edge 28 is contiguous withcentral zone 12, and has an external diameter D₂ that is approximately3.5 mm. Intermediate zone 14 is formed to have a first intermediate zonespherical radius R₂, which, when taken with the base curve radius,produces a first intermediate zone power of P₂. A second intermediatezone 16 with an outer edge 30 is contiguous with first intermediate zone14 and with zone 18. Intermediate zone 16 is formed to have a secondintermediate zone spherical radius R₃, which, when taken with the basecurve radius, produces a second intermediate zone power of P₃. Theintermediate zones typically improve the ability of the lens wearer tofocus intermediate distances.

Powers P₂ and P₃ are typically chosen so that P₁, P₂, P₃, and P₄ form amonotonic progression, typically a relatively smooth monotonicprogression such as a progression that may be defined by an algebraicfunction giving values of P₂, P₃ in terms of P₁ and P₄. In someembodiments of the present invention, powers P₂ and P₃ are averages ofpowers P₁ and P₄, the averages typically being weighted so that P₁, P₂,P₃, and P₄ form a substantially linear progression. Thus, powers P₂ andP₃ are typically derived according to the following equations:$\begin{matrix}{P_{2} = \frac{\left( {{2P_{1}} + P_{4}} \right)}{3}} & (1) \\{P_{3} = \frac{\left( {P_{1} + {2\quad P_{4}}} \right)}{3}} & (2)\end{matrix}$

For example, if the preset value by which P₄ is less than P₁ isapproximately 1.25 diopters, approximate values for P₂, P₃, and P₄ interms of P₁ are given by:P₂≈P₁−0.42   (3)P₃≈P₁−0.83   (4)

In this case, for a lens 10 which is to be produced for a presbyope witha near correction of +6.25 diopters, the values of P₁, P₂, P₃, and P₄are respectively approximately +6.25 Ds, +5.83 Ds, +5.42 Ds, and +5.00Ds.

The expressions of equations (1)-(4) apply for powers P₂ and P₃ when theprogression P₁, P₂, P₃, and P₄ is a substantially linear progression.Those skilled in the art will be able to derive equations for P₂ and P₃,in terms of P₁ and P₄, for other types of monotonic progression of P₁,P₂, P₃, and P₄, such as a logarithmic or a geometric progression.

The powers of each zone are produced by configuring each zone with thezone s respective radius of curvature R₁, R₂, R₃, and R₄. Tables I-IVbelow give values of R₁, R₂, R₃, and R₄ for different near corrections(N) corresponding to P₁, which the inventors have found in practice givepowers corresponding to equations (1) and (2). Values in the tables arefor base curves of surface 22 having a radius of 8.5, 8.732, and 9.1 mm,and differences (P₁-P₄) equal to 1.25 Ds and 2.00 Ds. Tables I-IV alsogive a center thickness (C. T.) for each lens. The center thickness iscalculated assuming that the edge of the lens has a thickness of 0.14mm. TABLE I Base curve radius = 8.5 mm; (P₁-P₄) = 1.25 Ds First SecondCentral Intermediate Intermediate N zone zone zone Outer zone (P₁) (R₁)(R₂) (R₃) (R₄) C.T. 20.00 4.0157 4.1084 4.2010 4.2936 1.1905 19.754.0362 4.1287 4.2212 4.3138 1.1642 19.50 4.0570 4.1494 4.2419 4.33431.1387 19.25 4.0782 4.1705 4.2628 4.3551 1.1139 19.00 4.0997 4.19194.2841 4.3763 1.0898 18.75 4.1217 4.2137 4.3058 4.3979 1.0664 18.504.1439 4.2359 4.3278 4.4197 1.0436 18.25 4.1665 4.2583 4.3501 4.44191.0214 18.00 4.1895 4.2811 4.3727 4.4644 0.9998 17.75 4.2128 4.30424.3957 4.4872 0.9787 17.50 4.2364 4.3277 4.4189 4.5102 0.9581 17.254.2603 4.3514 4.4425 4.5336 0.9379 17.00 4.2845 4.3754 4.4663 4.55720.9183 16.75 4.3091 4.3998 4.4905 4.5812 0.8991 16.50 4.3339 4.42444.5149 4.6054 0.8802 16.25 4.3591 4.4494 4.5396 4.6298 0.8618 16.004.3846 4.4746 4.5646 4.6546 0.8438 15.75 4.4103 4.5001 4.5898 4.67960.8262 15.50 4.4364 4.5259 4.6154 4.7049 0.8089 15.25 4.4627 4.55194.6412 4.7304 0.7919 15.00 4.4893 4.5783 4.6672 4.7561 0.7753 14.754.5162 4.6049 4.6935 4.7822 0.7590 14.50 4.5434 4.6318 4.7201 4.80840.7430 14.25 4.5709 4.6589 4.7469 4.8349 0.7273 14.00 4.5986 4.68634.7740 4.8617 0.7119 13.75 4.6266 4.7140 4.8013 4.8887 0.6967 13.504.6549 4.7419 4.8289 4.9159 0.6819 13.25 4.6835 4.7701 4.8567 4.94330.6673 13.00 4.7123 4.7985 4.8848 4.9710 0.6529 12.75 4.7413 4.82724.9131 4.9989 0.6388 12.50 4.7707 4.8561 4.9416 5.0270 0.6249 12.254.8003 4.8853 4.9703 5.0554 0.6113 12.00 4.8301 4.9147 4.9993 5.08390.5979 11.75 4.8602 4.9444 5.0285 5.1127 0.5847 11.50 4.8905 4.97435.0580 5.1417 0.5717 11.25 4.9211 5.0044 5.0876 5.1709 0.5589 11.004.9519 5.0347 5.1175 5.2003 0.5463 10.75 4.9830 5.0653 5.1476 5.22990.5340 10.50 5.0143 5.0961 5.1779 5.2597 0.5218 10.25 5.0459 5.12715.2084 5.2897 0.5098 10.00 5.0776 5.1584 5.2391 5.3198 0.4980 9.755.1096 5.1898 5.2700 5.3502 0.4864 9.50 5.1418 5.2215 5.3011 5.38080.4749 9.25 5.1743 5.2534 5.3324 5.4115 0.4637 9.00 5.2069 5.2854 5.36395.4424 0.4526 8.75 5.2398 5.3177 5.3956 5.4735 0.4416 8.50 5.2729 5.35025.4275 5.5048 0.4309 8.25 5.3062 5.3829 5.4595 5.5362 0.4203 8.00 5.33975.4157 5.4918 5.5678 0.4098 7.75 5.3734 5.4488 5.5242 5.5996 0.3995 7.505.4072 5.4820 5.5567 5.6315 0.3893 7.25 5.4413 5.5154 5.5895 5.66350.3793 7.00 5.4756 5.5490 5.6224 5.6957 0.3695 6.75 5.5100 5.5827 5.65545.7281 0.3598 6.50 5.5446 5.6166 5.6886 5.7606 0.3502 6.25 5.5794 5.65075.7219 5.7932 0.3408 6.00 5.6144 5.6849 5.7554 5.8260 0.3315 5.75 5.64955.7193 5.7891 5.8589 0.3223 5.50 5.6848 5.7538 5.8228 5.8919 0.3133 5.255.7202 5.7884 5.8567 5.9250 0.3043 5.00 5.7557 5.8232 5.8907 5.95820.2956 4.75 5.7914 5.8581 5.9248 5.9915 0.2869 4.50 5.8273 5.8932 5.95916.0250 0.2784 4.25 5.8632 5.9283 5.9934 6.0585 0.2700 4.00 5.8993 5.96366.0279 6.0921 0.2617 3.75 5.9355 5.9989 6.0624 6.1258 0.2535 3.50 5.97186.0344 6.0970 6.1596 0.2455 3.25 6.0082 6.0700 6.1317 6.1935 0.2376 3.006.0447 6.1056 6.1665 6.2274 0.2297 2.75 6.0813 6.1413 6.2013 6.26130.2220 2.50 6.1179 6.1771 6.2362 6.2954 0.2144 2.25 6.1546 6.2129 6.27126.3294 0.2070 2.00 6.1914 6.2488 6.3062 6.3635 0.1996 1.75 6.2283 6.28476.3412 6.3977 0.1923 1.50 6.2651 6.3207 6.3763 6.4319 0.1852 1.25 6.30216.3567 6.4114 6.4660 0.1781 1.00 6.3389 6.3927 6.4464 6.5001 0.1707 0.756.3759 6.4287 6.4815 6.5343 0.1639 0.50 6.4128 6.4647 6.5166 6.56850.1572 0.25 6.4498 6.5008 6.5518 6.6027 0.1505 0.00 6.4882 6.5382 6.58826.6383 0.1500 −0.25 6.5243 6.5734 6.6225 6.6716 0.1400 −0.50 6.56276.6108 6.6590 6.7071 0.1400 −0.75 6.6010 6.6482 6.6954 6.7426 0.1400−1.00 6.6392 6.6855 6.7318 6.7781 0.1400 −1.25 6.6774 6.7227 6.76816.8134 0.1400 −1.50 6.7154 6.7598 6.8042 6.8486 0.1400 −1.75 6.75346.7969 6.8403 6.8838 0.1400 −2.00 6.7912 6.8338 6.8763 6.9188 0.1400−2.25 6.8290 6.8705 6.9121 6.9537 0.1400 −2.50 6.8665 6.9072 6.94786.9885 0.1400 −2.75 6.9040 6.9437 6.9834 7.0231 0.1400 −3.00 6.94126.9800 7.0188 7.0576 0.1400 −3.25 6.9783 7.0162 7.0541 7.0920 0.1400−3.50 7.0152 7.0522 7.0892 7.1262 0.1400 −3.75 7.0519 7.0880 7.12417.1602 0.1400 −4.00 7.0884 7.1236 7.1588 7.1940 0.1400 −4.25 7.12477.1590 7.1933 7.2276 0.1400 −4.50 7.1608 7.1942 7.2276 7.2611 0.1400−4.75 7.1966 7.2291 7.2617 7.2943 0.1400 −5.00 7.2321 7.2638 7.29557.3272 0.1400 −5.25 7.2673 7.2982 7.3291 7.3600 0.1400 −5.50 7.30237.3324 7.3624 7.3925 0.1400 −5.75 7.3370 7.3662 7.3955 7.4247 0.1400−6.00 7.3713 7.3998 7.4282 7.4567 0.1400 −6.25 7.4053 7.4330 7.46077.4884 0.1400 −6.50 7.4390 7.4660 7.4929 7.5198 0.1400 −6.75 7.47237.4985 7.5247 7.5509 0.1400 −7.00 7.5053 7.5308 7.5562 7.5817 0.1400−7.25 7.5379 7.5626 7.5874 7.6122 0.1400 −7.50 7.5700 7.5941 7.61827.6424 0.1400 −7.75 7.6018 7.6252 7.6487 7.6722 0.1400 −8.00 7.63317.6560 7.6788 7.7016 0.1400 −8.25 7.6640 7.6862 7.7085 7.7307 0.1400−8.50 7.6945 7.7161 7.7378 7.7594 0.1400 −8.75 7.7244 7.7455 7.76667.7877 0.1400 −9.00 7.7539 7.7745 7.7951 7.8157 0.1400 −9.25 7.78297.8030 7.8231 7.8432 0.1400 −9.50 7.8114 7.8310 7.8507 7.8703 0.1400−9.75 7.8394 7.8586 7.8778 7.8970 0.1400 −10.00 7.8668 7.8856 7.90447.9232 0.1400 −10.25 7.8937 7.9121 7.9306 7.9490 0.1400 −10.50 7.92007.9381 7.9562 7.9743 0.1400 −10.75 7.9457 7.9635 7.9814 7.9992 0.1400−11.00 7.9709 7.9884 8.0060 8.0236 0.1400 −11.25 7.9954 8.0128 8.03018.0474 0.1400 −11.50 8.0194 8.0365 8.0537 8.0708 0.1400 −11.75 8.04278.0597 8.0767 8.0937 0.1400 −12.00 8.0653 8.0822 8.0991 8.1160 0.1400−12.25 8.0873 8.1042 8.1210 8.1378 0.1400 −12.50 8.1087 8.1255 8.14238.1591 0.1400 −12.75 8.1294 8.1462 8.1630 8.1798 0.1400 −13.00 8.14948.1662 8.1831 8.2000 0.1400 −13.25 8.1687 8.1856 8.2026 8.2196 0.1400−13.50 8.1873 8.2044 8.2215 8.2386 0.1400 −13.75 8.2051 8.2224 8.23978.2570 0.1400 −14.00 8.2223 8.2398 8.2573 8.2748 0.1400 −14.25 8.23878.2565 8.2742 8.2920 0.1400 −14.50 8.2543 8.2724 8.2905 8.3086 0.1400−14.75 8.2692 8.2877 8.3062 8.3246 0.1400 −15.00 8.2834 8.3022 8.32118.3400 0.1400 −15.25 8.2967 8.3161 8.3354 8.3547 0.1400 −15.50 8.30938.3291 8.3490 8.3688 0.1400 −15.75 8.3211 8.3415 8.3619 8.3822 0.1400−16.00 8.3321 8.3531 8.3740 8.3950 0.1400 −16.25 8.3423 8.3639 8.38558.4071 0.1400 −16.50 8.3517 8.3740 8.3963 8.4186 0.1400 −16.75 8.36038.3833 8.4063 8.4293 0.1400 −17.00 8.3681 8.3919 8.4156 8.4394 0.1400−17.25 8.3750 8.3996 8.4242 8.4488 0.1400 −17.50 8.3812 8.4066 8.43218.4576 0.1400 −17.75 8.3864 8.4128 8.4392 8.4656 0.1400 −18.00 8.39098.4182 8.4456 8.4729 0.1400 −18.25 8.3945 8.4229 8.4512 8.4796 0.1400−18.50 8.3973 8.4267 8.4561 8.4855 0.1400 −18.75 8.3992 8.4297 8.46028.4907 0.1400 −19.00 8.4003 8.4320 8.4636 8.4952 0.1400 −19.25 8.40068.4334 8.4662 8.4991 0.1400 −19.50 8.4000 8.4341 8.4681 8.5021 0.1400−19.75 8.3986 8.4339 8.4692 8.5045 0.1400 −20.00 8.3963 8.4330 8.46968.5062 0.1400

TABLE II Base curve radius = 8.5 mm; (P₁-P₄) = 2.00 Ds First SecondCentral Intermediate Intermediate N zone zone zone Outer zone (P₁) (R₁)(R₂) (R₃) (R₄) C.T. 20.00 3.9844 4.0877 4.1909 4.2942 1.1929 19.754.0044 4.1077 4.2110 4.3143 1.1666 19.50 4.0248 4.1281 4.2315 4.33481.1411 19.25 4.0455 4.1489 4.2523 4.3557 1.1163 19.00 4.0666 4.17004.2735 4.3769 1.0922 18.75 4.0880 4.1915 4.2950 4.3984 1.0688 18.504.1098 4.2133 4.3168 4.4203 1.0460 18.25 4.1319 4.2354 4.3389 4.44251.0238 18.00 4.1544 4.2579 4.3614 4.4649 1.0022 17.75 4.1771 4.28074.3842 4.4877 0.9811 17.50 4.2002 4.3037 4.4073 4.5108 0.9605 17.254.2236 4.3271 4.4306 4.5341 0.9403 17.00 4.2473 4.3508 4.4543 4.55780.9207 16.75 4.2714 4.3748 4.4783 4.5817 0.9014 16.50 4.2957 4.39914.5025 4.6059 0.8826 16.25 4.3203 4.4236 4.5270 4.6304 0.8642 16.004.3452 4.4485 4.5518 4.6551 0.8462 15.75 4.3704 4.4736 4.5769 4.68010.8285 15.50 4.3958 4.4990 4.6022 4.7054 0.8113 15.25 4.4216 4.52474.6278 4.7309 0.7943 15.00 4.4476 4.5506 4.6537 4.7567 0.7777 14.754.4739 4.5769 4.6798 4.7827 0.7614 14.50 4.5005 4.6033 4.7062 4.80900.7454 14.25 4.5273 4.6301 4.7328 4.8355 0.7297 14.00 4.5545 4.65704.7596 4.8622 0.7142 13.75 4.5818 4.6843 4.7868 4.8892 0.6991 13.504.6095 4.7118 4.8141 4.9164 0.6842 13.25 4.6374 4.7395 4.8417 4.94390.6696 13.00 4.6655 4.7675 4.8695 4.9716 0.6553 12.75 4.6939 4.79584.8976 4.9995 0.6411 12.50 4.7226 4.8242 4.9259 5.0276 0.6273 12.254.7515 4.8530 4.9544 5.0559 0.6136 12.00 4.7806 4.8819 4.9832 5.08450.6002 11.75 4.8100 4.9111 5.0122 5.1133 0.5870 11.50 4.8396 4.94055.0414 5.1422 0.5740 11.25 4.8695 4.9701 5.0708 5.1714 0.5613 11.004.8996 5.0000 5.1004 5.2008 0.5487 10.75 4.9299 5.0301 5.1302 5.23040.5363 10.50 4.9605 5.0604 5.1603 5.2602 0.5241 10.25 4.9912 5.09095.1905 5.2902 0.5122 10.00 5.0222 5.1216 5.2210 5.3204 0.5003 9.755.0534 5.1525 5.2517 5.3508 0.4887 9.50 5.0849 5.1837 5.2825 5.38130.4773 9.25 5.1165 5.2150 5.3135 5.4120 0.4660 9.00 5.1484 5.2466 5.34485.4430 0.4549 8.75 5.1804 5.2783 5.3762 5.4741 0.4440 8.50 5.2127 5.31025.4078 5.5053 0.4332 8.25 5.2451 5.3423 5.4395 5.5367 0.4226 8.00 5.27785.3746 5.4715 5.5683 0.4121 7.75 5.3106 5.4071 5.5036 5.6001 0.4018 7.505.3436 5.4397 5.5359 5.6320 0.3917 7.25 5.3768 5.4726 5.5683 5.66410.3817 7.00 5.4102 5.5056 5.6009 5.6963 0.3718 6.75 5.4437 5.5387 5.63375.7286 0.3621 6.50 5.4774 5.5720 5.6666 5.7611 0.3525 6.25 5.5113 5.60555.6996 5.7937 0.3431 6.00 5.5454 5.6391 5.7328 5.8265 0.3338 5.75 5.57955.6728 5.7661 5.8594 0.3246 5.50 5.6139 5.7067 5.7995 5.8924 0.3156 5.255.6483 5.7407 5.8331 5.9255 0.3067 5.00 5.6829 5.7749 5.8668 5.95870.2979 4.75 5.7177 5.8091 5.9006 5.9921 0.2892 4.50 5.7525 5.8435 5.93456.0255 0.2807 4.25 5.7875 5.8780 5.9685 6.0590 0.2723 4.00 5.8226 5.91266.0026 6.0927 0.2640 3.75 5.8578 5.9473 6.0368 6.1264 0.2558 3.50 5.89315.9821 6.0711 6.1601 0.2478 3.25 5.9284 6.0169 6.1055 6.1940 0.2399 3.005.9639 6.0519 6.1399 6.2279 0.2320 2.75 5.9994 6.0869 6.1744 6.26190.2243 2.50 6.0350 6.1220 6.2089 6.2959 0.2168 2.25 6.0707 6.1571 6.24356.3300 0.2093 2.00 6.1064 6.1923 6.2782 6.3641 0.2019 1.75 6.1422 6.22756.3129 6.3982 0.1946 1.50 6.1780 6.2628 6.3476 6.4324 0.1875 1.25 6.21386.2981 6.3823 6.4666 0.1804 1.00 6.2496 6.3333 6.4170 6.5007 0.1730 0.756.2855 6.3686 6.4517 6.5349 0.1662 0.50 6.3213 6.4039 6.4865 6.56910.1595 0.25 6.3572 6.4392 6.5212 6.6032 0.1528 0.00 6.3939 6.4754 6.55686.6383 0.1500 −0.25 6.4290 6.5099 6.5908 6.6716 0.1403 −0.50 6.46626.5465 6.6268 6.7071 0.1400 −0.75 6.5034 6.5831 6.6629 6.7426 0.1400−1.00 6.5405 6.6197 6.6989 6.7781 0.1400 −1.25 6.5775 6.6561 6.73486.8134 0.1400 −1.50 6.6144 6.6925 6.7706 6.8486 0.1400 −1.75 6.65126.7287 6.8063 6.8838 0.1400 −2.00 6.6879 6.7649 6.8418 6.9188 0.1400−2.25 6.7245 6.8009 6.8773 6.9537 0.1400 −2.50 6.7609 6.8368 6.91266.9885 0.1400 −2.75 6.7972 6.8725 6.9478 7.0231 0.1400 −3.00 6.83336.9081 6.9829 7.0576 0.1400 −3.25 6.8693 6.9435 7.0178 7.0920 0.1400−3.50 6.9050 6.9787 7.0525 7.1262 0.1400 −3.75 6.9406 7.0138 7.08707.1602 0.1400 −4.00 6.9759 7.0486 7.1213 7.1940 0.1400 −4.25 7.01107.0832 7.1554 7.2276 0.1400 −4.50 7.0459 7.1176 7.1893 7.2611 0.1400−4.75 7.0806 7.1518 7.2230 7.2943 0.1400 −5.00 7.1150 7.1857 7.25657.3272 0.1400 −5.25 7.1491 7.2194 7.2897 7.3600 0.1400 −5.50 7.18297.2528 7.3226 7.3925 0.1400 −5.75 7.2164 7.2859 7.3553 7.4247 0.1400−6.00 7.2497 7.3187 7.3877 7.4567 0.1400 −6.25 7.2826 7.3512 7.41987.4884 0.1400 −6.50 7.3151 7.3834 7.4516 7.5198 0.1400 −6.75 7.34737.4152 7.4831 7.5509 0.1400 −7.00 7.3792 7.4467 7.5142 7.5817 0.1400−7.25 7.4107 7.4779 7.5450 7.6122 0.1400 −7.50 7.4418 7.5086 7.57557.6424 0.1400 −7.75 7.4724 7.5390 7.6056 7.6722 0.1400 −8.00 7.50277.5690 7.6353 7.7016 0.1400 −8.25 7.5326 7.5986 7.6647 7.7307 0.1400−8.50 7.5620 7.6278 7.6936 7.7594 0.1400 −8.75 7.5909 7.6565 7.72217.7877 0.1400 −9.00 7.6194 7.6848 7.7502 7.8157 0.1400 −9.25 7.64747.7126 7.7779 7.8432 0.1400 −9.50 7.6749 7.7400 7.8052 7.8703 0.1400−9.75 7.7018 7.7669 7.8319 7.8970 0.1400 −10.00 7.7283 7.7933 7.85837.9232 0.1400 −10.25 7.7542 7.8192 7.8841 7.9490 0.1400 −10.50 7.77967.8445 7.9094 7.9743 0.1400 −10.75 7.8045 7.8694 7.9343 7.9992 0.1400−11.00 7.8287 7.8937 7.9586 8.0236 0.1400 −11.25 7.8524 7.9174 7.98248.0474 0.1400 −11.50 7.8755 7.9406 8.0057 8.0708 0.1400 −11.75 7.89807.9632 8.0284 8.0937 0.1400 −12.00 7.9198 7.9852 8.0506 8.1160 0.1400−12.25 7.9410 8.0066 8.0722 8.1378 0.1400 −12.50 7.9616 8.0274 8.09338.1591 0.1400 −12.75 7.9816 8.0476 8.1137 8.1798 0.1400 −13.00 8.00088.0672 8.1336 8.2000 0.1400 −13.25 8.0194 8.0861 8.1528 8.2196 0.1400−13.50 8.0373 8.1044 8.1715 8.2386 0.1400 −13.75 8.0545 8.1220 8.18958.2570 0.1400 −14.00 8.0711 8.1390 8.2069 8.2748 0.1400 −14.25 8.08698.1553 8.2236 8.2920 0.1400 −14.50 8.1020 8.1708 8.2397 8.3086 0.1400−14.75 8.1163 8.1857 8.2552 8.3246 0.1400 −15.00 8.1299 8.1999 8.27008.3400 0.1400 −15.25 8.1428 8.2134 8.2841 8.3547 0.1400 −15.50 8.15498.2262 8.2975 8.3688 0.1400 −15.75 8.1663 8.2383 8.3102 8.3822 0.1400−16.00 8.1769 8.2496 8.3223 8.3950 0.1400 −16.25 8.1867 8.2602 8.33368.4071 0.1400 −16.50 8.1958 8.2700 8.3443 8.4186 0.1400 −16.75 8.20408.2791 8.3542 8.4293 0.1400 −17.00 8.2115 8.2875 8.3635 8.4394 0.1400−17.25 8.2182 8.2951 8.3720 8.4488 0.1400 −17.50 8.2241 8.3019 8.37978.4576 0.1400 −17.75 8.2292 8.3080 8.3868 8.4656 0.1400 −18.00 8.23358.3133 8.3931 8.4729 0.1400 −18.25 8.2369 8.3178 8.3987 8.4796 0.1400−18.50 8.2396 8.3216 8.4035 8.4855 0.1400 −18.75 8.9415 8.3246 8.40778.4907 0.1400 −19.00 8.2426 8.3268 8.4110 8.4952 0.1400 −19.25 8.24288.3282 8.4136 8.4991 0.1400 −19.50 8.2422 8.3289 8.4155 8.5021 0.1400−19.75 8.2409 8.3288 8.4166 8.5045 0.1400 −20.00 8.2387 8.3279 8.41708.5062 0.1400

TABLE III Base curve radius = 8.732 mm; (P₁-P₄) = 1.25 Ds First SecondCentral Intermediate Intermediate N zone zone zone Outer zone (P₁) (R₁)(R₂) (R₃) (R₄) C.T. 20.00 4.0652 4.1608 4.2563 4.3519 1.1583 19.754.0868 4.1823 4.2778 4.3733 1.1335 19.50 4.1088 4.2042 4.2996 4.39501.1094 19.25 4.1311 4.2264 4.3217 4.4171 1.0860 19.00 4.1538 4.24904.3442 4.4394 1.0631 18.75 4.1768 4.2719 4.3670 4.4622 1.0409 18.504.2002 4.2952 4.3902 4.4852 1.0192 18.25 4.2240 4.3188 4.4137 4.50850.9981 18.00 4.2481 4.3428 4.4375 4.5322 0.9774 17.75 4.2725 4.36704.4616 4.5561 0.9572 17.50 4.2972 4.3916 4.4860 4.5804 0.9375 17.254.3223 4.4165 4.5107 4.6049 0.9182 17.00 4.3476 4.4417 4.5357 4.62980.8993 16.75 4.3733 4.4672 4.5610 4.6549 0.8809 16.50 4.3994 4.49304.5866 4.6803 0.8628 16.25 4.4257 4.5191 4.6125 4.7060 0.8451 16.004.4523 4.5455 4.6387 4.7319 0.8277 15.75 4.4792 4.5722 4.6652 4.75810.8107 15.50 4.5065 4.5992 4.6919 4.7846 0.7940 15.25 4.5340 4.62654.7189 4.8114 0.7776 15.00 4.5618 4.6540 4.7462 4.8384 0.7615 14.754.5899 4.6818 4.7737 4.8657 0.7458 14.50 4.6183 4.7100 4.8016 4.89320.7303 14.25 4.6470 4.7383 4.8296 4.9209 0.7151 14.00 4.6760 4.76704.8580 4.9490 0.7001 13.75 4.7053 4.7959 4.8866 4.9772 0.6854 13.504.7348 4.8251 4.9155 5.0058 0.6710 13.25 4.7647 4.8546 4.9446 5.03450.6568 13.00 4.7948 4.8843 4.9739 5.0635 0.6429 12.75 4.8251 4.91435.0035 5.0927 0.6291 12.50 4.8558 4.9446 5.0334 5.1222 0.6156 12.254.8867 4.9751 5.0635 5.1519 0.6024 12.00 4.9179 5.0059 5.0939 5.18180.5893 11.75 4.9494 5.0369 5.1244 5.2120 0.5765 11.50 4.9811 5.06825.1553 5.2424 0.5638 11.25 5.0131 5.0997 5.1863 5.2730 0.5513 11.005.0453 5.1315 5.2176 5.3038 0.5391 10.75 5.0778 5.1635 5.2491 5.33480.5270 10.50 5.1105 5.1957 5.2809 5.3660 0.5151 10.25 5.1435 5.22825.3128 5.3975 0.5034 10.00 5.1768 5.2609 5.3450 5.4291 0.4919 9.755.2102 5.2938 5.3774 5.4610 0.4805 9.50 5.2440 5.3270 5.4100 5.49310.4693 9.25 5.2779 5.3604 5.4428 5.5253 0.4583 9.00 5.3121 5.3940 5.47595.5577 0.4474 8.75 5.3465 5.4278 5.5091 5.5904 0.4367 8.50 5.3812 5.46185.5425 5.6232 0.4262 8.25 5.4160 5.4961 5.5761 5.6562 0.4158 8.00 5.45115.5305 5.6100 5.6894 0.4056 7.75 5.4864 5.5652 5.6440 5.7227 0.3955 7.505.5220 5.6001 5.6781 5.7562 0.3855 7.25 5.5577 5.6351 5.7125 5.78990.3757 7.00 5.5936 5.6703 5.7471 5.8238 0.3660 6.75 5.6297 5.7057 5.78185.8578 0.3565 6.50 5.6660 5.7413 5.8167 5.8920 0.3471 6.25 5.7025 5.77715.8517 5.9263 0.3379 6.00 5.7392 5.8131 5.8869 5.9607 0.3287 5.75 5.77615.8492 5.9222 5.9953 0.3197 5.50 5.8131 5.8854 5.9577 6.0300 0.3108 5.255.8503 5.9219 5.9934 6.0649 0.3021 5.00 5.8877 5.9584 6.0292 6.09990.2935 4.75 5.9252 5.9951 6.0651 6.1350 0.2850 4.50 5.9629 6.0320 6.10116.1702 0.2766 4.25 6.0007 6.0690 6.1372 6.2055 0.2683 4.00 6.0386 6.10616.1735 6.2409 0.2602 3.75 6.0767 6.1433 6.2099 6.2765 0.2522 3.50 6.11496.1806 6.2463 6.3121 0.2442 3.25 6.1532 6.2181 6.2829 6.3478 0.2364 3.006.1916 6.2556 6.3196 6.3835 0.2287 2.75 6.2302 6.2932 6.3563 6.41940.2212 2.50 6.2688 6.3309 6.3931 6.4553 0.2137 2.25 6.3075 6.3687 6.43006.4912 0.2063 2.00 6.3462 6.4066 6.4669 6.5272 0.1991 1.75 6.3851 6.44456.5039 6.5633 0.1919 1.50 6.4239 6.4824 6.5409 6.5994 0.1849 1.25 6.46296.5204 6.5780 6.6355 0.1779 1.00 6.5018 6.5584 6.6150 6.6716 0.1706 0.756.5408 6.5964 6.6521 6.7077 0.1639 0.50 6.5798 6.6345 6.6892 6.74390.1573 0.25 6.6189 6.6726 6.7263 6.7800 0.1507 0.00 6.6592 6.7120 6.76476.8175 0.1500 −0.25 6.6974 6.7492 6.8010 6.8528 0.1400 −0.50 6.73796.7887 6.8395 6.8903 0.1400 −0.75 6.7783 6.8281 6.8779 6.9278 0.1400−1.00 6.8186 6.8675 6.9163 6.9652 0.1400 −1.25 6.8589 6.9068 6.95467.0025 0.1400 −1.50 6.8991 6.9460 6.9928 7.0397 0.1400 −1.75 6.93916.9851 7.0310 7.0769 0.1400 −2.00 6.9791 7.0240 7.0690 7.1139 0.1400−2.25 7.0190 7.0629 7.1069 7.1508 0.1400 −2.50 7.0587 7.1017 7.14477.1876 0.1400 −2.75 7.0982 7.1403 7.1823 7.2243 0.1400 −3.00 7.13777.1787 7.2198 7.2608 0.1400 −3.25 7.1769 7.2170 7.2571 7.2972 0.1400−3.50 7.2159 7.2551 7.2942 7.3334 0.1400 −3.75 7.2548 7.2930 7.33127.3694 0.1400 −4.00 7.2934 7.3307 7.3680 7.4053 0.1400 −4.25 7.33197.3682 7.4046 7.4409 0.1400 −4.50 7.3700 7.4055 7.4409 7.4764 0.1400−4.75 7.4080 7.4425 7.4770 7.5116 0.1400 −5.00 7.4456 7.4793 7.51297.5466 0.1400 −5.25 7.4830 7.5158 7.5485 7.5813 0.1400 −5.50 7.52017.5520 7.5839 7.6158 0.1400 −5.75 7.5569 7.5879 7.6190 7.6500 0.1400−6.00 7.5933 7.6236 7.6538 7.6840 0.1400 −6.25 7.6295 7.6589 7.68837.7177 0.1400 −6.50 7.6652 7.6938 7.7224 7.7510 0.1400 −6.75 7.70067.7284 7.7563 7.7841 0.1400 −7.00 7.7356 7.7627 7.7898 7.8169 0.1400−7.25 7.7702 7.7966 7.8229 7.8493 0.1400 −7.50 7.8044 7.8301 7.85577.8813 0.1400 −7.75 7.8382 7.8632 7.8881 7.9131 0.1400 −8.00 7.87157.8958 7.9201 7.9444 0.1400 −8.25 7.9044 7.9280 7.9517 7.9754 0.1400−8.50 7.9368 7.9598 7.9829 8.0059 0.1400 −8.75 7.9687 7.9912 8.01368.0361 0.1400 −9.00 8.0001 8.0220 8.0439 8.0659 0.1400 −9.25 8.03108.0524 8.0738 8.0952 0.1400 −9.50 8.0613 8.0822 8.1031 8.1241 0.1400−9.75 8.0911 8.1116 8.1320 8.1525 0.1400 −10.00 8.1203 8.1404 8.16048.1805 0.1400 −10.25 8.1490 8.1686 8.1883 8.2080 0.1400 −10.50 8.17708.1963 8.2157 8.2350 0.1400 −10.75 8.2045 8.2235 8.2425 8.2615 0.1400−11.00 8.2313 8.2500 8.2688 8.2875 0.1400 −11.25 8.2575 8.2760 8.29458.3130 0.1400 −11.50 8.2830 8.3013 8.3196 8.3379 0.1400 −11.75 8.30798.3260 8.3442 8.3624 0.1400 −12.00 8.3321 8.3501 8.3682 8.3862 0.1400−12.25 8.3556 8.3736 8.3915 8.4095 0.1400 −12.50 8.3784 8.3963 8.41438.4322 0.1400 −12.75 8.4005 8.4184 8.4364 8.4544 0.1400 −13.00 8.42188.4399 8.4579 8.4759 0.1400 −13.25 8.4425 8.4606 8.4787 8.4968 0.1400−13.50 8.4623 8.4806 8.4989 8.5171 0.1400 −13.75 8.4814 8.4999 8.51848.5368 0.1400 −14.00 8.4997 8.5185 8.5372 8.5559 0.1400 −14.25 8.51738.5363 8.5553 8.5743 0.1400 −14.50 8.5340 8.5534 8.5727 8.5921 0.1400−14.75 8.5500 8.5697 8.5894 8.6092 0.1400 −15.00 8.5651 8.5852 8.60548.6256 0.1400 −15.25 8.5794 8.6000 8.6207 8.6414 0.1400 −15.50 8.59288.6140 8.6352 8.6564 0.1400 −15.75 8.6055 8.6272 8.6490 8.6708 0.1400−16.00 8.6172 8.6396 8.6621 8.6845 0.1400 −16.25 8.6281 8.6512 8.67448.6975 0.1400 −16.50 8.6382 8.6620 8.6859 8.7097 0.1400 −16.75 8.64748.6720 8.6966 8.7212 0.1400 −17.00 8.6557 8.6812 8.7066 8.7321 0.1400−17.25 8.6631 8.6895 8.7158 8.7421 0.1400 −17.50 8.6697 8.6969 8.72428.7515 0.1400 −17.75 8.6753 8.7036 8.7318 8.7601 0.1400 −18.00 8.68018.7094 8.7387 8.7679 0.1400 −18.25 8.6840 8.7143 8.7447 8.7751 0.1400−18.50 8.6870 8.7184 8.7499 8.7814 0.1400 −18.75 8.6890 8.7217 8.75448.7870 0.1400 −19.00 8.6902 8.7241 8.7580 8.7918 0.1400 −19.25 8.69058.7256 8.7608 8.7959 0.1400 −19.50 8.6899 8.7263 8.7628 8.7992 0.1400−19.75 8.6884 8.7262 8.7640 8.8018 0.1400 −20.00 8.6859 8.7251 8.76448.8036 0.1400

TABLE IV Base curve radius = 8.732 mm; (P₁-P₄) = 2.00 Ds First SecondCentral Intermediate Intermediate N zone zone zone Outer zone (P₁) (R₁)(R₂) (R₃) (R₄) C.T. 20.00 4.0329 4.1394 4.2460 4.3525 1.1608 19.754.0540 4.1606 4.2672 4.3738 1.1359 19.50 4.0755 4.1822 4.2889 4.39561.1118 19.25 4.0974 4.2041 4.3109 4.4176 1.0884 19.00 4.1196 4.22644.3332 4.4400 1.0656 18.75 4.1421 4.2490 4.3558 4.4627 1.0433 18.504.1650 4.2719 4.3788 4.4857 1.0216 18.25 4.1882 4.2952 4.4021 4.50911.0005 18.00 4.2118 4.3188 4.4258 4.5327 0.9798 17.75 4.2357 4.34274.4497 4.5567 0.9596 17.50 4.2599 4.3669 4.4739 4.5809 0.9399 17.254.2844 4.3914 4.4985 4.6055 0.9206 17.00 4.3092 4.4162 4.5233 4.63030.9017 16.75 4.3343 4.4414 4.5484 4.6554 0.8833 16.50 4.3598 4.46684.5738 4.6808 0.8652 16.25 4.3855 4.4925 4.5995 4.7065 0.8475 16.004.4115 4.5185 4.6255 4.7325 0.8301 15.75 4.4379 4.5448 4.6517 4.75870.8131 15.50 4.4645 4.5714 4.6783 4.7852 0.7964 15.25 4.4914 4.59824.7051 4.8119 0.7800 15.00 4.5186 4.6254 4.7322 4.8389 0.7639 14.754.5461 4.6528 4.7595 4.8662 0.7481 14.50 4.5739 4.6805 4.7871 4.89370.7326 14.25 4.6019 4.7084 4.8150 4.9215 0.7174 14.00 4.6302 4.73674.8431 4.9495 0.7025 13.75 4.6588 4.7651 4.8715 4.9778 0.6878 13.504.6877 4.7939 4.9001 5.0063 0.6734 13.25 4.7168 4.8229 4.9290 5.03510.6592 13.00 4.7462 4.8522 4.9581 5.0641 0.6452 12.75 4.7759 4.88174.9875 5.0933 0.6315 12.50 4.8058 4.9115 5.0171 5.1228 0.6180 12.254.8360 4.9415 5.0470 5.1525 0.6047 12.00 4.8665 4.9718 5.0771 5.18240.5916 11.75 4.8972 5.0023 5.1074 5.2125 0.5788 11.50 4.9282 5.03315.1380 5.2429 0.5661 11.25 4.9594 5.0641 5.1688 5.2735 0.5537 11.004.9908 5.0953 5.1998 5.3043 0.5414 10.75 5.0225 5.1268 5.2311 5.33530.5293 10.50 5.0545 5.1585 5.2625 5.3666 0.5175 10.25 5.0867 5.19045.2942 5.3980 0.5057 10.00 5.1191 5.2226 5.3261 5.4297 0.4942 9.755.1517 5.2550 5.3583 5.4615 0.4829 9.50 5.1846 5.2876 5.3906 5.49360.4717 9.25 5.2177 5.3204 5.4231 5.5258 0.4606 9.00 5.2511 5.3535 5.45595.5583 0.4498 8.75 5.2846 5.3867 5.4888 5.5909 0.4391 8.50 5.3184 5.42025.5219 5.6237 0.4285 8.25 5.3524 5.4538 5.5553 5.6567 0.4181 8.00 5.38655.4877 5.5888 5.6899 0.4079 7.75 5.4209 5.5217 5.6225 5.7233 0.3978 7.505.4555 5.5559 5.6564 5.7568 0.3878 7.25 5.4903 5.5904 5.6904 5.79050.3780 7.00 5.5253 5.6250 5.7246 5.8243 0.3684 6.75 5.5605 5.6598 5.75905.8583 0.3588 6.50 5.5958 5.6947 5.7936 5.8925 0.3494 6.25 5.6313 5.72985.8283 5.9268 0.3402 6.00 5.6670 5.7651 5.8632 5.9613 0.3310 5.75 5.70295.8006 5.8982 5.9958 0.3220 5.50 5.7389 5.8362 5.9334 6.0306 0.3132 5.255.7751 5.8719 5.9687 6.0654 0.3044 5.00 5.8115 5.9078 6.0041 6.10040.2958 4.75 5.8479 5.9438 6.0397 6.1355 0.2873 4.50 5.8846 5.9799 6.07536.1707 0.2789 4.25 5.9213 6.0162 6.1111 6.2060 0.2706 4.00 5.9582 6.05266.1470 6.2415 0.2625 3.75 5.9952 6.0891 6.1831 6.2770 0.2545 3.50 6.03236.1257 6.2192 6.3126 0.2465 3.25 6.0695 6.1624 6.2554 6.3483 0.2387 3.006.1068 6.1992 6.2916 6.3841 0.2310 2.75 6.1442 6.2361 6.3280 6.41990.2235 2.50 6.1817 6.2731 6.3644 6.4558 0.2160 2.25 6.2193 6.3101 6.40096.4918 0.2086 2.00 6.2569 6.3472 6.4375 6.5278 0.2014 1.75 6.2946 6.38436.4741 6.5638 0.1942 1.50 6.3323 6.4215 6.5107 6.5999 0.1872 1.25 6.37016.4587 6.5474 6.6360 0.1802 1.00 6.4078 6.4959 6.5840 6.6721 0.1729 0.756.4456 6.5332 6.6207 6.7082 0.1662 0.50 6.4835 6.5704 6.6574 6.74440.1596 0.25 6.5213 6.6077 6.6941 6.7806 0.1530 0.00 6.5599 6.6458 6.73166.8175 0.1500 −0.25 6.5971 6.6824 6.7676 6.8529 0.1406 −0.50 6.63626.7209 6.8056 6.8903 0.1400 −0.75 6.6754 6.7595 6.8436 6.9278 0.1400−1.00 6.7145 6.7980 6.8816 6.9652 0.1400 −1.25 6.7535 6.8365 6.91957.0025 0.1400 −1.50 6.7924 6.8749 6.9573 7.0397 0.1400 −1.75 6.83136.9132 6.9950 7.0769 0.1400 −2.00 6.8700 6.9513 7.0326 7.1139 0.1400−2.25 6.9086 6.9894 7.0701 7.1508 0.1400 −2.50 6.9471 7.0273 7.10757.1876 0.1400 −2.75 6.9854 7.0650 7.1447 7.2243 0.1400 −3.00 7.02367.1027 7.1817 7.2608 0.1400 −3.25 7.0615 7.1401 7.2186 7.2972 0.1400−3.50 7.0993 7.1774 7.2554 7.3334 0.1400 −3.75 7.1369 7.2144 7.29197.3694 0.1400 −4.00 7.1743 7.2513 7.3283 7.4053 0.1400 −4.25 7.21157.2880 7.3644 7.4409 0.1400 −4.50 7.2484 7.3244 7.4004 7.4764 0.1400−4.75 7.2851 7.3606 7.4361 7.5116 0.1400 −5.00 7.3215 7.3965 7.47167.5466 0.1400 −5.25 7.3577 7.4322 7.5068 7.5813 0.1400 −5.50 7.39357.4676 7.5417 7.6158 0.1400 −5.75 7.4291 7.5027 7.5764 7.6500 0.1400−6.00 7.4643 7.5375 7.6108 7.6840 0.1400 −6.25 7.4992 7.5720 7.64487.7177 0.1400 −6.50 7.5337 7.6062 7.6786 7.7510 0.1400 −6.75 7.56797.6400 7.7120 7.7841 0.1400 −7.00 7.6017 7.6734 7.7451 7.8169 0.1400−7.25 7.6351 7.7065 7.7779 7.8493 0.1400 −7.50 7.6681 7.7392 7.81037.8813 0.1400 −7.75 7.7007 7.7715 7.8423 7.9131 0.1400 −8.00 7.73297.8034 7.8739 7.9444 0.1400 −8.25 7.7646 7.8348 7.9051 7.9754 0.1400−8.50 7.7958 7.8659 7.9359 8.0059 0.1400 −8.75 7.8266 7.8964 7.96638.0361 0.1400 −9.00 7.8569 7.9265 7.9962 8.0659 0.1400 −9.25 7.88677.9562 8.0257 8.0952 0.1400 −9.50 7.9159 7.9853 8.0547 8.1241 0.1400−9.75 7.9446 8.0139 8.0832 8.1525 0.1400 −10.00 7.9728 8.0420 8.11138.1805 0.1400 −10.25 8.0004 8.0696 8.1388 8.2080 0.1400 −10.50 8.02758.0966 8.1658 8.2350 0.1400 −10.75 8.0539 8.1231 8.1923 8.2615 0.1400−11.00 8.0798 8.1490 8.2183 8.2875 0.1400 −11.25 8.1050 8.1743 8.24378.3130 0.1400 −11.50 8.1296 8.1990 8.2685 8.3379 0.1400 −11.75 8.15358.2231 8.2927 8.3624 0.1400 −12.00 8.1768 8.2466 8.3164 8.3862 0.1400−12.25 8.1995 8.2695 8.3395 8.4095 0.1400 −12.50 8.2214 8.2917 8.36208.4322 0.1400 −12.75 8.2427 8.3132 8.3838 8.4544 0.1400 −13.00 8.26328.3341 8.4050 8.4759 0.1400 −13.25 8.2831 8.3543 8.4256 8.4968 0.1400−13.50 8.3022 8.3738 8.4455 8.5171 0.1400 −13.75 8.3206 8.3927 8.46488.5368 0.1400 −14.00 8.3382 8.4108 8.4833 8.5559 0.1400 −14.25 8.35518.4282 8.5012 8.5743 0.1400 −14.50 8.3712 8.4448 8.5184 8.5921 0.1400−14.75 8.3865 8.4607 8.5350 8.6092 0.1400 −15.00 8.4011 8.4759 8.55088.6256 0.1400 −15.25 8.4148 8.4903 8.5658 8.6414 0.1400 −15.50 8.42788.5040 8.5802 8.6564 0.1400 −15.75 8.4399 8.5169 8.5938 8.6708 0.1400−16.00 8.4512 8.5290 8.6067 8.6845 0.1400 −16.25 8.4617 8.5403 8.61898.6975 0.1400 −16.50 8.4714 8.5508 8.6303 8.7097 0.1400 −16.75 8.48028.5606 8.6409 8.7212 0.1400 −17.00 8.4882 8.5695 8.6508 8.7321 0.1400−17.25 8.4954 8.5776 8.6599 8.7421 0.1400 −17.50 8.5017 8.5849 8.66828.7515 0.1400 −17.75 8.5071 8.5914 8.6758 8.7601 0.1400 −18.00 8.51178.5971 8.6825 8.7679 0.1400 −18.25 8.5154 8.6020 8.6885 8.7751 0.1400−18.50 8.5183 8.6060 8.6937 8.7814 0.1400 −18.75 8.5203 8.6092 8.69818.7870 0.1400 −19.00 8.5214 8.6116 8.7017 8.7918 0.1400 −19.25 8.52178.6131 8.7045 8.7959 0.1400 −19.50 8.5211 8.6138 8.7065 8.7992 0.1400−19.75 8.5196 8.6137 8.7077 8.8018 0.1400 −20.00 8.5173 8.6127 8.70818.8036 0.1400

TABLE V Base curve radius = 9.1 mm; (P₁-P₄) = 1.25 Ds First SecondCentral Intermediate Intermediate N zone zone zone Outer zone (P₁) (R₁)(R₂) (R₃) (R₄) C.T. 20.00 4.1430 4.2432 4.3434 4.4436 1.1163 19.754.1663 4.2665 4.3666 4.4668 1.0934 19.50 4.1900 4.2901 4.3902 4.49031.0710 19.25 4.2140 4.3141 4.4141 4.5141 1.0492 19.00 4.2384 4.33844.4383 4.5383 1.0280 18.75 4.2632 4.3630 4.4629 4.5628 1.0072 18.504.2883 4.3880 4.4878 4.5876 0.9869 18.25 4.3137 4.4134 4.5131 4.61270.9671 18.00 4.3395 4.4391 4.5386 4.6382 0.9476 17.75 4.3656 4.46514.5645 4.6639 0.9287 17.50 4.3921 4.4914 4.5907 4.6900 0.9101 17.254.4189 4.5180 4.6172 4.7164 0.8919 17.00 4.4460 4.5450 4.6440 4.74300.8740 16.75 4.4735 4.5723 4.6711 4.7700 0.8565 16.50 4.5012 4.59994.6986 4.7972 0.8394 16.25 4.5293 4.6278 4.7263 4.8247 0.8226 16.004.5578 4.6560 4.7543 4.8526 0.8061 15.75 4.5865 4.6846 4.7826 4.88070.7899 15.50 4.6156 4.7134 4.8112 4.9091 0.7740 15.25 4.6450 4.74254.8401 4.9377 0.7583 15.00 4.6746 4.7720 4.8693 4.9667 0.7430 14.754.7046 4.8017 4.8988 4.9959 0.7279 14.50 4.7350 4.8318 4.9286 5.02540.7131 14.25 4.7656 4.8621 4.9586 5.0551 0.6985 14.00 4.7965 4.89274.9889 5.0852 0.6842 13.75 4.8277 4.9236 5.0196 5.1155 0.6701 13.504.8593 4.9549 5.0504 5.1460 0.6563 13.25 4.8911 4.9864 5.0816 5.17680.6426 13.00 4.9233 5.0181 5.1130 5.2079 0.6292 12.75 4.9557 5.05025.1447 5.2392 0.6160 12.50 4.9884 5.0826 5.1767 5.2708 0.6030 12.255.0214 5.1152 5.2089 5.3027 0.5903 12.00 5.0548 5.1481 5.2414 5.33480.5777 11.75 5.0884 5.1813 5.2742 5.3671 0.5653 11.50 5.1222 5.21475.3072 5.3997 0.5531 11.25 5.1564 5.2485 5.3405 5.4325 0.5410 11.005.1909 5.2824 5.3740 5.4656 0.5292 10.75 5.2256 5.3167 5.4078 5.49890.5175 10.50 5.2606 5.3512 5.4418 5.5324 0.5060 10.25 5.2959 5.38605.4761 5.5662 0.4947 10.00 5.3315 5.4211 5.5106 5.6002 0.4835 9.755.3674 5.4564 5.5454 5.6344 0.4725 9.50 5.4035 5.4919 5.5804 5.66890.4617 9.25 5.4398 5.5277 5.6156 5.7035 0.4510 9.00 5.4765 5.5638 5.65115.7384 0.4404 8.75 5.5134 5.6001 5.6868 5.7735 0.4301 8.50 5.5505 5.63665.7227 5.8088 0.4198 8.25 5.5879 5.6734 5.7588 5.8443 0.4097 8.00 5.62555.7104 5.7952 5.8800 0.3998 7.75 5.6634 5.7476 5.8318 5.9160 0.3900 7.505.7016 5.7851 5.8686 5.9521 0.3803 7.25 5.7399 5.8227 5.9056 5.98840.3707 7.00 5.7785 5.8606 5.9427 6.0249 0.3613 6.75 5.8173 5.8987 5.98016.0615 0.3520 6.50 5.8564 5.9370 6.0177 6.0984 0.3429 6.25 5.8956 5.97566.0555 6.1354 0.3339 6.00 5.9351 6.0143 6.0934 6.1726 0.3250 5.75 5.97486.0532 6.1316 6.2099 0.3162 5.50 6.0147 6.0923 6.1699 6.2474 0.3076 5.256.0548 6.1315 6.2083 6.2851 0.2990 5.00 6.0950 6.1710 6.2470 6.32290.2906 4.75 6.1355 6.2106 6.2857 6.3609 0.2823 4.50 6.1761 6.2504 6.32476.3990 0.2741 4.25 6.2169 6.2903 6.3638 6.4372 0.2661 4.00 6.2578 6.33046.4030 6.4756 0.2581 3.75 6.2990 6.3706 6.4423 6.5140 0.2503 3.50 6.34026.4110 6.4818 6.5526 0.2425 3.25 6.3816 6.4515 6.5214 6.5913 0.2349 3.006.4232 6.4921 6.5611 6.6301 0.2274 2.75 6.4648 6.5329 6.6009 6.66890.2200 2.50 6.5066 6.5737 6.6408 6.7079 0.2126 2.25 6.5485 6.6146 6.68086.7469 0.2054 2.00 6.5905 6.6557 6.7209 6.7861 0.1983 1.75 6.6326 6.69686.7610 6.8252 0.1913 1.50 6.6747 6.7380 6.8012 6.8645 0.1844 1.25 6.71706.7792 6.8415 6.9037 0.1776 1.00 6.7592 6.8204 6.8817 6.9430 0.1705 0.756.8015 6.8618 6.9220 6.9823 0.1639 0.50 6.8439 6.9032 6.9624 7.02170.1574 0.25 6.8864 6.9446 7.0028 7.0610 0.1510 0.00 6.9300 6.9872 7.04447.1016 0.1500 −0.25 6.9716 7.0278 7.0840 7.1401 0.1400 −0.50 7.01557.0706 7.1258 7.1809 0.1400 −0.75 7.0593 7.1134 7.1675 7.2216 0.1400−1.00 7.1031 7.1562 7.2092 7.2623 0.1400 −1.25 7.1468 7.1988 7.25097.3029 0.1400 −1.50 7.1904 7.2414 7.2924 7.3434 0.1400 −1.75 7.23407.2840 7.3339 7.3839 0.1400 −2.00 7.2775 7.3264 7.3753 7.4242 0.1400−2.25 7.3208 7.3687 7.4166 7.4645 0.1400 −2.50 7.3641 7.4109 7.45787.5046 0.1400 −2.75 7.4072 7.4530 7.4988 7.5446 0.1400 −3.00 7.45017.4949 7.5397 7.5844 0.1400 −3.25 7.4929 7.5366 7.5804 7.6242 0.1400−3.50 7.5355 7.5782 7.6210 7.6637 0.1400 −3.75 7.5779 7.6196 7.66137.7031 0.1400 −4.00 7.6201 7.6608 7.7015 7.7422 0.1400 −4.25 7.66207.7018 7.7415 7.7812 0.1400 −4.50 7.7037 7.7425 7.7813 7.8200 0.1400−4.75 7.7452 7.7830 7.8208 7.8586 0.1400 −5.00 7.7864 7.8232 7.86017.8969 0.1400 −5.25 7.8273 7.8632 7.8991 7.9350 0.1400 −5.50 7.86797.9029 7.9378 7.9728 0.1400 −5.75 7.9082 7.9422 7.9763 8.0103 0.1400−6.00 7.9481 7.9813 8.0144 8.0476 0.1400 −6.25 7.9877 8.0200 8.05238.0845 0.1400 −6.50 8.0270 8.0584 8.0898 8.1212 0.1400 −6.75 8.06588.0964 8.1269 8.1575 0.1400 −7.00 8.1042 8.1340 8.1637 8.1935 0.1400−7.25 8.1422 8.1712 8.2002 8.2291 0.1400 −7.50 8.1798 8.2080 8.23628.2644 0.1400 −7.75 8.2169 8.2444 8.2718 8.2993 0.1400 −8.00 8.25368.2803 8.3070 8.3338 0.1400 −8.25 8.2897 8.3158 8.3418 8.3679 0.1400−8.50 8.3254 8.3508 8.3761 8.4015 0.1400 −8.75 8.3605 8.3853 8.41008.4348 0.1400 −9.00 8.3951 8.4192 8.4434 8.4676 0.1400 −9.25 8.42918.4527 8.4763 8.4999 0.1400 −9.50 8.4625 8.4856 8.5087 8.5318 0.1400−9.75 8.4954 8.5180 8.5406 8.5631 0.1400 −10.00 8.5276 8.5498 8.57198.5940 0.1400 −10.25 8.5592 8.5810 8.6027 8.6244 0.1400 −10.50 8.59028.6116 8.6329 8.6542 0.1400 −10.75 8.6205 8.6415 8.6625 8.6835 0.1400−11.00 8.6502 8.6709 8.6916 8.7123 0.1400 −11.25 8.6791 8.6995 8.72008.7405 0.1400 −11.50 8.7073 8.7276 8.7478 8.7681 0.1400 −11.75 8.73488.7549 8.7750 8.7951 0.1400 −12.00 8.7616 8.7815 8.8015 8.8215 0.1400−12.25 8.7876 8.8075 8.8274 8.8473 0.1400 −12.50 8.8128 8.8327 8.85258.8724 0.1400 −12.75 8.8373 8.8572 8.8770 8.8969 0.1400 −13.00 8.86098.8809 8.9008 8.9208 0.1400 −13.25 8.8837 8.9038 8.9239 8.9440 0.1400−13.50 8.9057 8.9260 8.9463 8.9665 0.1400 −13.75 8.9269 8.9474 8.96798.9884 0.1400 −14.00 8.9472 8.9680 8.9887 9.0095 0.1400 −14.25 8.96678.9877 9.0088 9.0299 0.1400 −14.50 8.9852 9.0067 9.0282 9.0496 0.1400−14.75 9.0029 9.0248 9.0467 9.0686 0.1400 −15.00 9.0197 9.0421 9.06459.0869 0.1400 −15.25 9.0355 9.0585 9.0814 9.1043 0.1400 −15.50 9.05059.0740 9.0975 9.1211 0.1400 −15.75 9.0645 9.0887 9.1129 9.1371 0.1400−16.00 9.0776 9.1025 9.1273 9.1522 0.1400 −16.25 9.0897 9.1153 9.14109.1667 0.1400 −16.50 9.1008 9.1273 9.1538 9.1803 0.1400 −16.75 9.11109.1384 9.1657 9.1931 0.1400 −17.00 9.1203 9.1486 9.1768 9.2051 0.1400−17.25 9.1285 9.1578 9.1871 9.2163 0.1400 −17.50 9.1358 9.1661 9.19649.2267 0.1400 −17.75 9.1421 9.1735 9.2049 9.2363 0.1400 −18.00 9.14749.1799 9.2125 9.2450 0.1400 −18.25 9.1517 9.1854 9.2192 9.2529 0.1400−18.50 9.1550 9.1900 9.2250 9.2600 0.1400 −18.75 9.1573 9.1936 9.22999.2662 0.1400 −19.00 9.1586 9.1963 9.2339 9.2716 0.1400 −19.25 9.15899.1980 9.2371 9.2761 0.1400 −19.50 9.1582 9.1988 9.2393 9.2798 0.1400−19.75 9.1565 9.1986 9.2406 9.2827 0.1400 −20.00 9.1539 9.1975 9.24119.2846 0.1400

TABLE VI Base curve radius = 9.1 mm; (P₁-P₄) = 2.00 Ds First SecondCentral Intermediate Intermediate N zone zone zone Outer zone (P₁) (R₁)(R₂) (R₃) (R₄) C.T. 20.00 4.1092 4.2209 4.3325 4.4442 1.1187 19.754.1320 4.2438 4.3556 4.4673 1.0958 19.50 4.1551 4.2670 4.3789 4.49081.0734 19.25 4.1787 4.2907 4.4027 4.5147 1.0516 19.00 4.2025 4.31464.4267 4.5388 1.0303 18.75 4.2267 4.3389 4.4511 4.5633 1.0096 18.504.2513 4.3636 4.4759 4.5882 0.9893 18.25 4.2762 4.3885 4.5009 4.61330.9694 18.00 4.3014 4.4138 4.5263 4.6387 0.9500 17.75 4.3269 4.43954.5520 4.6645 0.9310 17.50 4.3528 4.4654 4.5780 4.6905 0.9124 17.254.3790 4.4917 4.6043 4.7169 0.8942 17.00 4.4056 4.5182 4.6309 4.74360.8764 16.75 4.4324 4.5451 4.6578 4.7705 0.8589 16.50 4.4596 4.57234.6850 4.7978 0.8418 16.25 4.4871 4.5998 4.7125 4.8253 0.8249 16.004.5148 4.6276 4.7404 4.8531 0.8084 15.75 4.5429 4.6557 4.7685 4.88120.7922 15.50 4.5714 4.6841 4.7969 4.9096 0.7763 15.25 4.6001 4.71284.8255 4.9383 0.7607 15.00 4.6291 4.7418 4.8545 4.9672 0.7453 14.754.6584 4.7711 4.8838 4.9964 0.7303 14.50 4.6880 4.8007 4.9133 5.02590.7154 14.25 4.7179 4.8305 4.9431 5.0557 0.7009 14.00 4.7481 4.86074.9732 5.0857 0.6866 13.75 4.7787 4.8911 5.0035 5.1160 0.6725 13.504.8095 4.9218 5.0342 5.1466 0.6586 13.25 4.8405 4.9528 5.0651 5.17740.6450 13.00 4.8719 4.9841 5.0963 5.2084 0.6316 12.75 4.9036 5.01565.1277 5.2398 0.6184 12.50 4.9355 5.0475 5.1594 5.2714 0.6054 12.254.9678 5.0796 5.1914 5.3032 0.5926 12.00 5.0003 5.1119 5.2236 5.33530.5800 11.75 5.0331 5.1446 5.2561 5.3676 0.5676 11.50 5.0661 5.17755.2889 5.4002 0.5554 11.25 5.0995 5.2107 5.3219 5.4330 0.5434 11.005.1331 5.2441 5.3551 5.4661 0.5315 10.75 5.1670 5.2778 5.3886 5.49940.5198 10.50 5.2011 5.3117 5.4223 5.5329 0.5083 10.25 5.2355 5.34595.4563 5.5667 0.4970 10.00 5.2702 5.3804 5.4905 5.6007 0.4858 9.755.3051 5.4151 5.5250 5.6349 0.4748 9.50 5.3403 5.4500 5.5597 5.66940.4640 9.25 5.3758 5.4852 5.5946 5.7041 0.4533 9.00 5.4115 5.5206 5.62985.7389 0.4428 8.75 5.4474 5.5563 5.6652 5.7740 0.4324 8.50 5.4836 5.59225.7008 5.8093 0.4221 8.25 5.5200 5.6283 5.7366 5.8449 0.4120 8.00 5.55665.6646 5.7726 5.8806 0.4021 7.75 5.5935 5.7012 5.8088 5.9165 0.3923 7.505.6306 5.7380 5.8453 5.9526 0.3826 7.25 5.6680 5.7749 5.8819 5.98890.3730 7.00 5.7055 5.8121 5.9188 6.0254 0.3636 6.75 5.7433 5.8495 5.95586.0621 0.3544 6.50 5.7813 5.8871 5.9930 6.0989 0.3452 6.25 5.8194 5.92496.0304 6.1359 0.3362 6.00 5.8578 5.9629 6.0680 6.1731 0.3273 5.75 5.89646.0011 6.1058 6.2105 0.3185 5.50 5.9352 6.0394 6.1437 6.2480 0.3099 5.255.9741 6.0780 6.1818 6.2856 0.3013 5.00 6.0132 6.1166 6.2200 6.32350.2929 4.75 6.0525 6.1555 6.2585 6.3614 0.2846 4.50 6.0920 6.1945 6.29706.3995 0.2764 4.25 6.1316 6.2336 6.3357 6.4377 0.2684 4.00 6.1714 6.27296.3745 6.4761 0.2604 3.75 6.2113 6.3124 6.4135 6.5145 0.2526 3.50 6.25136.3519 6.4525 6.5531 0.2448 3.25 6.2915 6.3916 6.4917 6.5918 0.2372 3.006.3318 6.4314 6.5310 6.6306 0.2297 2.75 6.3722 6.4713 6.5704 6.66950.2222 2.50 6.4128 6.5113 6.6099 6.7084 0.2149 2.25 6.4534 6.5514 6.64946.7475 0.2077 2.00 6.4941 6.5916 6.6891 6.7866 0.2006 1.75 6.5349 6.63186.7288 6.8258 0.1936 1.50 6.5758 6.6722 6.7686 6.8650 0.1867 1.25 6.61676.7125 6.8084 6.9043 0.1799 1.00 6.6576 6.7529 6.8482 6.9435 0.1728 0.756.6986 6.7933 6.8881 6.9828 0.1662 0.50 6.7397 6.8338 6.9280 7.02220.1597 0.25 6.7807 6.8743 6.9680 7.0616 0.1533 0.00 6.8225 6.9156 7.00867.1016 0.1500 −0.25 6.8630 6.9555 7.0479 7.1404 0.1411 −0.50 6.90526.9971 7.0890 7.1809 0.1400 −0.75 6.9477 7.0390 7.1303 7.2216 0.1400−1.00 6.9901 7.0808 7.1716 7.2623 0.1400 −1.25 7.0324 7.1226 7.21277.3029 0.1400 −1.50 7.0747 7.1643 7.2539 7.3434 0.1400 −1.75 7.11687.2058 7.2949 7.3839 0.1400 −2.00 7.1589 7.2473 7.3358 7.4242 0.1400−2.25 7.2008 7.2887 7.3766 7.4645 0.1400 −2.50 7.2426 7.3300 7.41737.5046 0.1400 −2.75 7.2843 7.3711 7.4578 7.5446 0.1400 −3.00 7.32587.4120 7.4982 7.5844 0.1400 −3.25 7.3672 7.4528 7.5385 7.6242 0.1400−3.50 7.4084 7.4935 7.5786 7.6637 0.1400 −3.75 7.4493 7.5339 7.61857.7031 0.1400 −4.00 7.4901 7.5741 7.6582 7.7422 0.1400 −4.25 7.53067.6142 7.6977 7.7812 0.1400 −4.50 7.5709 7.6540 7.7370 7.8200 0.1400−4.75 7.6110 7.6935 7.7760 7.8586 0.1400 −5.00 7.6507 7.7328 7.81487.8969 0.1400 −5.25 7.6902 7.7718 7.8534 7.9350 0.1400 −5.50 7.72947.8105 7.8916 7.9728 0.1400 −5.75 7.7683 7.8489 7.9296 8.0103 0.1400−6.00 7.8068 7.8871 7.9673 8.0476 0.1400 −6.25 7.8450 7.9248 8.00478.0845 0.1400 −6.50 7.8828 7.9623 8.0417 8.1212 0.1400 −6.75 7.92037.9993 8.0784 8.1575 0.1400 −7.00 7.9573 8.0360 8.1148 8.1935 0.1400−7.25 7.9939 8.0723 8.1507 8.2291 0.1400 −7.50 8.0302 8.1082 8.18638.2644 0.1400 −7.75 8.0659 8.1437 8.2215 8.2993 0.1400 −8.00 8.10128.1787 8.2562 8.3338 0.1400 −8.25 8.1360 8.2133 8.2906 8.3679 0.1400−8.50 8.1704 8.2474 8.3245 8.4015 0.1400 −8.75 8.2042 8.2811 8.35798.4348 0.1400 −9.00 8.2375 8.3142 8.3909 8.4676 0.1400 −9.25 8.27028.3468 8.4233 8.4999 0.1400 −9.50 8.3024 8.3789 8.4553 8.5318 0.1400−9.75 8.3340 8.4104 8.4868 8.5631 0.1400 −10.00 8.3651 8.4414 8.51778.5940 0.1400 −10.25 8.3955 8.4718 8.5481 8.6244 0.1400 −10.50 8.42538.5016 8.5779 8.6542 0.1400 −10.75 8.4544 8.5308 8.6072 8.6835 0.1400−11.00 8.4829 8.5594 8.6358 8.7123 0.1400 −11.25 8.5107 8.5873 8.66398.7405 0.1400 −11.50 8.5379 8.6146 8.6913 8.7681 0.1400 −11.75 8.56438.6412 8.7181 8.7951 0.1400 −12.00 8.5900 8.6672 8.7443 8.8215 0.1400−12.25 8.6150 8.6924 8.7698 8.8473 0.1400 −12.50 8.6392 8.7170 8.79478.8724 0.1400 −12.75 8.6627 8.7408 8.8189 8.8969 0.1400 −13.00 8.68558.7639 8.8423 8.9208 0.1400 −13.25 8.7074 8.7863 8.8651 8.9440 0.1400−13.50 8.7285 8.8079 8.8872 8.9665 0.1400 −13.75 8.7488 8.8287 8.90858.9884 0.1400 −14.00 8.7684 8.8487 8.9291 9.0095 0.1400 −14.25 8.78708.8680 8.9490 9.0299 0.1400 −14.50 8.8048 8.8864 8.9680 9.0496 0.1400−14.75 8.8218 8.9041 8.9863 9.0686 0.1400 −15.00 8.8379 8.9209 9.00399.0869 0.1400 −15.25 8.8531 8.9369 9.0206 9.1043 0.1400 −15.50 8.86758.9520 9.0366 9.1211 0.1400 −15.75 8.8809 8.9663 9.0517 9.1371 0.1400−16.00 8.8935 8.9797 9.0660 9.1522 0.1400 −16.25 8.9051 8.9923 9.07959.1667 0.1400 −16.50 8.9158 9.0040 9.0921 9.1803 0.1400 −16.75 8.92569.0148 9.1039 9.1931 0.1400 −17.00 8.9345 9.0247 9.1149 9.2051 0.1400−17.25 8.9424 9.0337 9.1250 9.2163 0.1400 −17.50 8.9494 9.0418 9.13439.2267 0.1400 −17.75 8.9554 9.0490 9.1427 9.2363 0.1400 −18.00 8.96059.0553 9.1502 9.2450 0.1400 −18.25 8.9646 9.0607 9.1568 9.2529 0.1400−18.50 8.9678 9.0652 9.1626 9.2600 0.1400 −18.75 8.9700 9.0687 9.16759.2662 0.1400 −19.00 8.9713 9.0714 9.1715 9.2716 0.1400 −19.25 8.97169.0731 9.1746 9.2761 0.1400 −19.50 8.9709 9.0739 9.1769 9.2798 0.1400−19.75 8.9693 9.0737 9.1782 9.2827 0.1400 −20.00 8.9667 9.0727 9.17879.2846 0.1400

Typically, after production, lens 10 is checked to confirm that thepowers of zones 24, 14, 16, and 18 conform respectively to theprescribed near vision correction, the values given by equations (1) and(2) (if the linear progression described above with reference to theequations is applied), and the near vision correction less the presetvalue. If necessary, the spherical radius of the specific zones areadjusted so that the powers are in conformity with these values.

The inventors have found that multirange contact lenses producedaccording to the criteria described hereinabove, for a preset value of1.25 diopters, give good vision for distances from approximately 25 cmto infinity, for wearers having a range of distance corrections that areapproximately 0.6 to approximately 2.8 diopters less than the wearer'snear correction. For a preset value of 2.00 diopters, the range ofdistance corrections is approximately 1.5 to approximately 4.0 diopters.For all preset values, good vision occurs for a range of distancecorrections better than 2 diopters.

Lens 10 may be produced by any contact lens process known in the art,such as, but not limited to, cutting on a lathe or molding. Typically,radius transitions between zones, i.e., at zone edges 26, 28, and 30,are substantially sharp, and the method of production for lens 10 istypically chosen so as to give substantially sharp transitions.Consequently, within specific zones 24, 14, 16, and 18, each zone isformed to have a substantially constant power. The inventors have foundthat a process of molding gives suitably acute radius transitions.Alternatively, lens 10 may be formed by cutting on a lathe, followed bybuffing.

The description hereinabove for lens 10 has assumed that there are twointermediate annular zones between central zone 24 and the outer annularzone 18. It will be appreciated that the scope of the present inventionincludes whole numbers of intermediate annular zones other than two,wherein the powers of such intermediate zones form, when taken togetherwith the central zone power and the outer annular zone power, amonotonic progression.

In some embodiments of the present invention, near surface 22 isimplemented as a toric curve, e.g., to correct for astigmatism, thetoric curve having two different radii of curvature producing tworespective powers. Typically, two radii of curvature R₁, for each power,are calculated, and the values are averaged to find an actual value ofR₁. A similar averaging procedure is applied to find actual values touse for R₂, R₃, and R₄. The description with respect to FIG. 2 belowdescribes in more detail how embodiments of the present invention may beused to correct for astigmatism.

FIG. 2 is a schematic top view of a multirange contact lens 50,according to an embodiment of the present invention. Apart from thedifferences described below, the operation of lens 50 is generallysimilar to that of lens 10 (FIG. 1), such that parts of the lensesindicated by the same reference numerals in both lenses 50 and 10 aregenerally similar in construction and in operation.

Rather than having a single spherical curvature, as described above forlens 10, in lens 50 each of zones 24, 14, 16, and 18, has a firstcylindrical radius of curvature, R_(1a), R_(2a), R_(3a), and R_(4a)along an axis 52, and a second cylindrical radius of curvature R_(1b),R_(2b), R_(3b), and R_(4b) along an axis 54. Thus, each zone 24, 14, 16,and 18, acting together with near surface 22 having a single sphericalradius curvature, generates a first set of powers, P_(1a), P_(2a),P_(3a), and P_(4a) along axis 52, and a second set of powers, P_(1b),P_(2b), P_(3b), and P_(4b) along axis 54, so that lens 50 is able tocorrect astigmatism of a wearer of the lens.

It will be appreciated that astigmatism may also be corrected either byhaving near surface 22 have two different cylindrical radii of curvatureR_(basea), R_(baseb), or by each zone 24, 14, 16, and 18, of far surface12 having two different cylindrical radii of curvature (as describedhereinabove), or by both near surface 22 and the zones of far surface 12each having two different cylindrical radii of curvature.

Typically, the differences (P_(1a)-P_(1b)), (P_(2a)-P_(2b)),(P_(3a)-P_(3b)), and (P_(4a)-P_(4b)) are set to be approximately equal,and correspond with an astigmatic factor, also termed the “cylinder”value, of the eye of the lens wearer. Furthermore, the angle made byaxis 52 is assumed to correspond with the “axis” value of the lensprescription.

In use, for lens 50 to correctly compensate the astigmatism of the eyefor which it has been made, the lens must be maintained in alignment inthe user's eye, so that it does not rotate. Methods are known in the artfor maintaining the alignment, including weighting a lower edge of lens50 and/or removing a portion of an edge of the lens so that the act ofblinking aligns the lens. All such methods known in the art are assumedto be comprised within the scope of the present invention.

FIG. 3 shows schematic top views of multirange contact lenses 70, 72 and74 according to an embodiment of the present invention. Hereinbelow,lenses 70, 72, and 74 are also generically termed lenses 76. Apart fromthe differences described below, the operation of lenses 76 is generallysimilar to that of lens 10 (FIG. 1), such that parts of the lensesindicated by the same reference numerals in lenses 76 and in lens 10 aregenerally similar in construction and in operation. In addition tocompensating for the lack of accommodation typically occurring inpresbyopes by providing a lens that allows the user to focus near anddistant objects, each of lenses 76 improves the peripheral vision of theuser.

A number of factors are known to affect the ability of a person toperceive and respond to objects in the periphery of their direct gaze.Such factors include how well peripheral objects are focussed onto theretina. As described in more detail below, peripheral vision may beenhanced by forming one or more of the zones of each of lenses 76 tohave a non-circular edge shape.

In lens 70, zone 24 is configured to have an oval edge 80. In oneembodiment, edge 80 is typically approximately elliptical in shape,having a major axis 82 in an approximately horizontal direction. Duringuse of lens 70, axis 82 may be maintained in its horizontal alignment byone of the methods referred to above. Making zone 24 in the form of ahorizontally elongated oval improves a user's peripheral vision,particularly the peripheral vision of objects which are close to theuser, and which would be well focussed if they were directly observed bythe user. The improvement in peripheral vision is typically for objectsthat are in a horizontal peripheral region, corresponding to thehorizontal elongation of edge 80.

The principle of enhancing the peripheral vision by altering the shapeof one or more of the edges of one or more of zones 24, 14, 16, and/or18 to be non-circular may be advantageously applied in cases where auser is known to require a specific type of peripheral vision.

As a first example, illustrated by lens 72, if the user's occupation isas a driver, horizontal far field region peripheral vision may beimportant, so that the driver is quickly aware of distant objects viewedin one or more mirrors, while the gaze of the driver is directedstraight ahead. In this case, zone 18 of lens 72 may be configured as ahorizontally elongated oval, having an elongated outer edge 84.Optionally an edge 86, separating zones 18 and 16, may also beelongated, typically having a horizontal elongation as is illustrated inFIG. 3.

As a second example, illustrated by lens 74, the user may be abasketball player, where vertical medium field peripheral vision isimportant, so that the player is able to see the basket well, whilelooking at the floor. In this case zone 16 may be configured with avertically elongated periphery, having a vertically elongated outer edge88.

It will be appreciated that for zones other than central zone 24, theinner and/or the outer edge of the zone may be made non-circular. Itwill also be appreciated that the one or more non-circular edges of azone used to enhance peripheral vision do not need to have anyparticular symmetry, and may have no symmetry whatsoever. Thus, in lens72, edge 84 may be elongated more to the left than to the right, so asto enhance the peripheral vision on the left side of the driver morethan on the right side. Also, in lens 74, edge 88 may be elongated moreup than down, so that the basketball player's peripheral vision ispreferentially enhanced upwards.

In some embodiments of the present invention, the non-circular edge maybe used both to enhance peripheral vision, and also to maintain thealignment of the lens while it is in use. For example, in lens 72, eyeblinking may interact with the elongated oval zone 24 to maintain thelens horizontal.

It will be appreciated that a multirange contact lens combining theprinciples described above with reference to both FIG. 2 and FIG. 3 maybe implemented. Such a multirange lens is able to alter the peripheralvision and correct astigmatism of the wearer.

Contact lenses such as multirange contact lenses 10, 50, and 76, aretypically produced as described above, by using a transparent materialhaving one refractive index, and adjusting curvatures of the zones ofthe material to form the required different powers. Transparentmaterials having variable refractive indices are known in the art, suchas are used to produce graded index (GRIN) lenses, and a variablerefractive index material may be used to produce a multirange contactlens having powers substantially as described above for lenses 10, 50,and 76. All such lenses are assumed to be comprised within the scope ofthe present invention.

As will be appreciated by those skilled in the art, for any region of alens using a variable refractive index material, the curvature of thezone of the region, the base curve, and the range and distribution ofthe refractive index of the material between the zone and the base curveall contribute to the overall power generated for the region.

It will thus be appreciated that the power of any specific zone, thebase curve, and the transparent material therebetween, may be generatedby adjusting the curvature of the zone and the base curve, and byselecting an appropriate range and spatial distribution of therefractive indices of the transparent material.

FIG. 4 is a schematic cross-section of a mold 90, according to anembodiment of the present invention. It will be appreciated thatmultirange contact lenses 10, 50, and 76, or lenses incorporatingcombinations of the principles of operation thereof, improve vision byeffectively altering the existing corrective power of the eye upon whichthey are placed. The eye's corrective power is predominantly generatedby the cornea, with smaller contributions from the internal lens of theeye, and from the vitreous and aqueous humors. Altering the shape of thecornea so that it forms zones corresponding to zones 24, 14, 16, and 18,in both edge shape and in power, thus provides an alternative and/or anadditional method for improving the vision of the eye.

Mold 90 comprises an outer surface 92 which is generally sphericallycurved. The mold has an inner surface 94 which is generally in the formof zones 96, 98, 100, 102, the zones of the mold being formed to berespectively generally “female” versions of zones 24, 14, 16, 18, if thelatter are considered to be “males.” Zones 96, 98, 100, and 102 are alsogenerically referred to herein as mold zones 104. Mold 90 is positionedon the cornea of an eve, and zones 104 act to reshape the cornea so thatthe reshaped cornea corresponds with zones 24, 14, 16, 18. The mold istypically positioned on the cornea of the wearer before sleep.Alternatively or additionally, the wearer may position the mold on thecornea at any other suitable time.

Specific dimensions of each of zones 104 of mold 90 are typicallydetermined from initial measurements of curvature of the cornea of theeye of the wearer using the mold, and from calculated parameters for amultirange contact lens in the form of lens 10, 50 or one of lenses 76.New zonal curvatures for the cornea are then determined, usingrespective desired changes in power for each zone, and assuming arefractive index for the cornea approximately equal to 1.38.

For example, a presbyope is determined to have a corneal sphericalcurvature of 7.7 mm, and so has an unadjusted cornea power of 49.3 D. Itis determined that lens 10, having zone powers for zones 24, 14, 16, and18 of P₁=+6.25 Ds, P₂=+5.83 Ds, P₃=+5.42 Ds, and P₄=+5.00 Ds, wouldcorrect the vision of the presbyope. To reproduce the effect of lens 10,mold 90 is prepared. To effect the same power changes as the zones oflens 10, zones 96, 98, 100, and 102, have respective spherical radii ofcurvatures approximately equal to 6.84 mm, 6.89 mm, 6.94 mm, and 7.00mm. As for lens 10, zones 104 are typically formed to have substantiallysimilar circular outlines of approximate diameters 2.5 mm, 3.5 mm, 4.5mm, and 9 mm. However, rather than having generally sharp edges betweenthe zones, edges of mold zones 104 are typically rounded, to avoiddamage to the cornea.

If mold 90 is to replace a multirange lens such as lens 50 or one oflenses 76, those skilled in the art will be able to adapt theexplanation given above with respect to lens 10, mutatis mutandis, togenerate the required cylindrical radii of curvature and the dimensionsof edges of zones 104.

It will be appreciated that the embodiments described above are cited byway of example, and that the present invention is not limited to whathas been particularly shown and described hereinabove. Rather, the scopeof the present invention includes both combinations and subcombinationsof the various features described hereinabove, as well as variations andmodifications thereof which would occur to persons skilled in the artupon reading the foregoing description and which are not disclosed inthe prior art.

1-16. (canceled)
 17. A mold for shaping a cornea of a user of the mold,the mold including a surface which comprises: a central zone which iscurved and which is adapted to shape the cornea in a central cornealregion to have a central zone refractive power; an outer zone which iscurved and which is adapted to shape the cornea in an outer cornealregion to have an outer zone refractive power which is less than thecentral zone refractive power; and an intermediary region, intermediatethe central zone and the outer zone, comprising one or more contiguousintermediate zones, each of which is curved and which is adapted toshape the cornea to have respective one or more intermediate zonerefractive powers defining a monotonic progression of decreasingrefractive power from the central zone to the outer zone.
 18. The moldaccording to claim 17, wherein the central zone refractive power isselected to correct near vision of the user.
 19. The mold according toclaim 17, wherein the outer zone refractive power is betweenapproximately 1 diopter and approximately 2.5 diopters less than thecentral zone refractive power. 20-40. (canceled)
 41. A method forshaping a cornea, comprising: providing a mold having a surface whichcomprises: a central zone which is curved and which is adapted to shapethe cornea in a central corneal region to have a central zone refractivepower, an outer zone which is curved and which is adapted to shape thecornea in an outer corneal region to have an outer zone refractive powerwhich is less than the central zone refractive power, and anintermediary region, intermediate the central zone and the outer zone,comprising one or more contiguous intermediate zones, each of which iscurved and which is adapted to shape the cornea to have respective oneor more intermediate zone refractive powers defining a monotonicprogression of decreasing refractive power from the central zone to theouter zone; and applying the mold to the cornea.
 42. The methodaccording to claim 41, wherein the central zone refractive power isselected to correct near vision of the user.
 43. The method according toclaim 41, wherein the outer zone refractive power is betweenapproximately 1 diopter and approximately 2.5 diopters less than thecentral zone refractive power. 44.-48. (canceled)